Zoom lens and optical apparatus having the same

ABSTRACT

A zoom lens is constructed with, in order from an object side to an image side, a first lens unit of negative optical power, the first lens unit including a negative meniscus lens having a concave surface facing the image side and a positive meniscus lens having a convex surface facing the object side, a second lens unit of positive optical power, the second lens unit including a cemented lens of positive optical power as a whole disposed on the most image side of the second lens unit, and a lens having a concave surface facing the image side and adjoining a surface on the object side of the cemented lens, and a third lens unit of positive optical power, wherein a separation between the first lens unit and the second lens unit and a separation between the second lens unit and the third lens unit are varied to effect variation of magnification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens and an optical apparatushaving the zoom lens, and more particularly to a zoom lens suited for afilm still camera, a video camera, a digital still camera or the like,which has three lens units in which a lens unit of negative refractivepower leads, and which has the entirety of a lens system thereof reducedin size by appropriately setting the lens construction of the respectivelens units.

2. Description of Related Art

In recent years, with the advancement of high performance of an imagepickup apparatus (camera), such as a video camera or a digital stillcamera, using a solid-state image sensor, a zoom lens having a largeaperture ratio including a wide angle of view is desired for the purposeof being used for an optical system of such an image pickup apparatus.Since, in such an image pickup apparatus, a variety of optical members,including a low-pass filter, a color correction filter, etc., aredisposed between the rearmost portion of the zoom lens and the imagesensor, a lens system having a relatively long back focal distance isrequired for the optical system. In addition, in the case of a colorcamera using an image sensor for color images, a zoom lens excellent intelecentricity on the image side is desired for an optical system of thecolor camera so as to prevent color shading.

Heretofore, there have been proposed a variety of wide-angle two-unitzoom lenses of the so-called short zoom type each of which is composedof a first lens unit of negative refractive power and a second lens unitof positive refractive power, the separation between the first lens unitand the second lens unit being varied to effect the variation ofmagnification. In such an optical system of the short zoom type, thevariation of magnification is effected by moving the second lens unit ofpositive refractive power, and the compensation for the shift of animage point due to the variation of magnification is effected by movingthe first lens unit of negative refractive power.

In such a lens construction composed of two lens units, the zoommagnification thereof is 2× or thereabout. Further, in order to make theentirety of a lens system in a compact form while having a high variablemagnification ratio greater than 2×, there have been proposed, forexample, in Japanese Patent Publication No. Hei 7-3507 (corresponding toU.S. Pat. No. 4,810,072), Japanese Patent Publication No. Hei 6-40170(corresponding to U.S. Pat. No. 4,647,160), etc., the so-calledthree-unit zoom lenses in each of which a third lens unit of negative orpositive refractive power is disposed on the image side of the two-unitzoom lens so as to correct the various aberrations occurring due to thehigh variable magnification.

Further, in U.S. Pat. Nos. 4,828,372 and 5,262,897, there is disclosed athree-unit zoom lens in which the second lens unit is composed of sixlens elements, as a whole, including two cemented lenses, therebyattaining the high variable magnification of 3× or more.

Three-unit zoom lenses satisfying both the back focal distance and thetelecentric characteristic have been proposed in, for example, JapaneseLaid-Open Patent Application No. Sho 63-135913 (corresponding to U.S.Pat. No. 4,838,666), Japanese Laid-Open Patent Application No. Hei7-261083, etc. In addition, in Japanese Laid-Open Patent Application No.Hei 3-288113 (corresponding to U.S. Pat. No. 5,270,863), there isdisclosed a three-unit zoom lens in which a first lens unit of negativerefractive power is fixed and a second lens unit of positive refractivepower and a third lens unit of positive refractive power are moved toeffect the variation of magnification. However, in these zoom lenses,there are such drawbacks that the number of constituent lens elements ofeach lens unit is relatively large, the total length of the lens systemis great, and the production cost is high.

Further, in recent years, there has been widely used the so-calledbarrel-retractable zoom lens in which, in order to make the compactnessof a camera and the high magnification of a lens system compatible witheach other, the separation between the respective adjacent lens units atthe time of nonuse of the camera is reduced up to the separationdifferent from that at the time of use of the camera, thereby lesseningthe amount of protrusion of the zoom lens from the camera body. However,in a case where, as in the conventional zoom lenses, the number ofconstituent lens elements of each lens unit is large and, as a result,the length of each lens unit on the optical axis is great, or in a casewhere the amount of movement of each lens unit during zooming and duringfocusing is large and the total lens length is, therefore, great, it issometimes impossible to attain the desired length of the zoom lens asretracted.

Further, in the zoom lens disclosed in Japanese Laid-Open PatentApplication No. Hei 7-261083, a convex lens (positive lens) is disposedon the most object side of the first lens unit of negative refractivepower, so that there is such a drawback that an increase of the outerdiameter of the zoom lens when made to have a wide angle is inevitable.In addition, in this zoom lens, since the focusing onto a close objectis effected by moving the first lens unit of negative refractive power,there is such a drawback that the construction of a lens mountingmechanism is complicated in combination with the movement for zooming.

Further, in U.S. Pat. No. 4,999,007, there is disclosed a three-unitzoom lens in which each of the first lens unit and the second lens unitis composed of a single lens. However, in this zoom lens, the total lenslength at the wide-angle end is relatively great, and, because thedistance between the first lens unit and the stop at the wide-angle endis large, the height of incidence of an off-axial ray of light is largeto increase the diameter of a lens element of the first lens unit.Therefore, there is such a drawback that the entirety of a lens systembecomes large.

BRIEF SUMMARY OF THE INVENTION

In view of the above-mentioned drawbacks of the conventional zoomlenses, an object of the invention is to provide a zoom lens which issuited for a photographic system using a solid-state image sensor, has ahigh variable magnification ratio despite being compact and small indiameter with less constituent lens elements, and has excellent opticalperformance, and to provide an optical apparatus having the zoom lens.

To attain the above object, in accordance with an aspect of theinvention, there is provided a zoom lens, which comprises, in order froman object side to an image side, a first lens unit of negative opticalpower, the first lens unit including a negative meniscus lens having aconcave surface facing the image side and a positive meniscus lenshaving a convex surface facing the object side, a second lens unit ofpositive optical power, the second lens unit including a cemented lensof positive optical power as a whole disposed on the most image side ofthe second lens unit, and a lens having a concave surface facing theimage side and adjoining a surface on the object side of the cementedlens, and a third lens unit of positive optical power, wherein aseparation between the first lens unit and the second lens unit and aseparation between the second lens unit and the third lens unit arevaried to effect variation of magnification.

In accordance with another aspect of the invention, there is provided azoom lens, which comprises, in order from an object side to an imageside, a first lens unit of negative optical power, the first lens unitincluding a negative meniscus lens having a concave surface facing theimage side and a positive meniscus lens having a convex surface facingthe object side, a second lens unit of positive optical power, thesecond lens unit including a negative lens of bi-concave form, apositive lens disposed on the object side of the negative lens ofbi-concave form and having a convex surface facing the object side, anda cemented lens of positive optical power as a whole disposed on theimage side of the negative lens of bi-concave form, and a third lensunit of positive optical power, wherein a separation between the firstlens unit and the second lens unit and a separation between the secondlens unit and the third lens unit are varied to effect variation ofmagnification.

In accordance with a further aspect of the invention, there is provideda zoom lens, which comprises, in order from an object side to an imageside, a first lens unit of negative optical power, the first lens unitincluding a negative meniscus lens having a concave surface facing theimage side and a positive meniscus lens having a convex surface facingthe object side, a second lens unit of positive optical power, thesecond lens unit including, in order from the object side to the imageside, one or two positive lenses, a negative lens of bi-concave form,and a cemented lens of positive optical power as a whole, and a thirdlens unit of positive optical power, wherein a separation between thefirst lens unit and the second lens unit and a separation between thesecond lens unit and the third lens unit are varied to effect variationof magnification, and wherein the zoom lens satisfies the followingconditions:0.5<fc/f 2<2.00.5<(Ra+Rb)/(Ra−Rb)<2.50.3<|fn|/f 2<2.00.5<(Rd+Rc)/(Rd−Rc)<2.5where fc is a focal length of the cemented lens in the second lens unit,fn is a focal length of the negative lens in the second lens unit, f2 isa focal length of the second lens unit, Ra is a radius of curvature of asurface on the object side of the cemented lens in the second lens unit,Rb is a radius of curvature of a surface on the image side of thenegative lens in the second lens unit, and Rc and Rd are radii ofcurvature of lens surfaces on the object side and the image side,respectively, of the positive lens disposed on the most object side ofthe second lens unit.

In accordance with a still further aspect of the invention, there isprovided a zoom lens, which comprises, in order from an object side toan image side, a first lens unit of negative optical power, the firstlens unit including a negative lens and a positive lens, a second lensunit of positive optical power, the second lens unit consisting of acemented lens and one positive lens, and a third lens unit of positiveoptical power, the third lens unit including a positive lens, wherein aseparation between the first lens unit and the second lens unit and aseparation between the second lens unit and the third lens unit arevaried to effect variation of magnification.

In accordance with a still further aspect of the invention, there isprovided a zoom lens, which comprises, in order from an object side toan image side, a first lens unit of negative optical power, a secondlens unit of positive optical power, and a third lens unit of positiveoptical power, the third lens unit consisting of one or two lensesincluding a positive lens, wherein a separation between the first lensunit and the second lens unit and a separation between the second lensunit and the third lens unit are varied to effect variation ofmagnification, and wherein the zoom lens satisfies the followingconditions:ndp3<1.5vdp3>70.0where ndp3 and vdp3 are a refractive index and Abbe number,respectively, of material of the positive lens in the third lens unit.

In accordance with a still further aspect of the invention, there isprovided a zoom lens, which comprises, in order from an object side toan image side, a first lens unit of negative optical power, a secondlens unit of positive optical power, and a third lens unit of positiveoptical power, wherein a separation between the first lens unit and thesecond lens unit and a separation between the second lens unit and thethird lens unit are varied to effect variation of magnification, andwherein, during the variation of magnification from a wide-angle end toa telephoto end with an infinitely distant object focused on, the thirdlens unit moves monotonically toward the image side or moves with alocus convex toward the image side, and the zoom lens satisfies thefollowing condition:0.08<M 3/fw<0.4where M3 is an amount of movement of the third lens unit toward theimage side during the variation of magnification from the wide-angle endto the telephoto end with an infinitely distant object focused on, andfw is a focal length of the zoom lens at the wide-angle end.

In accordance with a still further aspect of the invention, there isprovided a zoom lens, which comprises, in order from an object side toan image side, a first lens unit of negative optical power, the firstlens unit consisting of, in order from the object side to the imageside, a negative lens and a positive lens, a second lens unit ofpositive optical power, and a third lens unit of positive optical power,wherein a separation between the first lens unit and the second lensunit and a separation between the second lens unit and the third lensunit are varied to effect variation of magnification, wherein, with aninfinitely distant object focused on, the third lens unit is locatednearer to the image side at a telephoto end than at a wide-angle end,and wherein the zoom lens satisfies the following condition:0.7<|f 1/ft|<1.0where f1 is a focal length of the first lens unit, and ft is a focallength of the zoom lens at the telephoto end.

In accordance with a still further aspect of the invention, there isprovided a zoom lens, which comprises, in order from an object side toan image side, a first lens. unit of negative optical power, the firstlens unit consisting of, in order from the object side to the imageside, a negative lens and a positive lens, a second lens unit ofpositive optical power, and a third lens unit of positive optical power,focusing being effected by moving the third lens unit, wherein aseparation between the first lens unit and the second lens unit and aseparation between the second lens unit and the third lens unit arevaried to effect variation of magnification, and wherein, during thevariation of magnification from a wide-angle end to a telephoto end withan infinitely distant object focused on, the third lens unit movesmonotonically toward the image side or moves with a locus convex towardthe image side, and the zoom lens satisfies the following conditions:0.08<M 3/fw<0.40.7<|f 1/ft|<1.01.45<f 3/ft<2.00.63<f 2/ft<0.8where M3 is an amount of movement of the third lens unit toward theimage side during the variation of magnification from the wide-angle endto the telephoto end with an infinitely distant object focused on, fwand ft are focal lengths of the zoom lens at the wide-angle end and thetelephoto end, respectively, and f1, f2 and f3 are focal lengths of thefirst lens unit, the second lens unit and the third lens unit,respectively.

Further, an optical apparatus according to the invention comprises azoom lens set forth in accordance with any one of the above aspects ofthe invention.

The above and further objects and features of the invention will becomeapparent from the following detailed description of preferredembodiments thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a lens block diagram showing a zoom lens at the wide-angle endaccording to a numerical example 1 of the invention.

FIGS. 2A to 2D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 1 of theinvention.

FIGS. 3A to 3D are graphs showing aberration curves at the middle focallength position in the zoom lens according to the numerical example 1 ofthe invention.

FIGS. 4A to 4D are graphs showing aberration curves at the telephoto endin the zoom lens according to the numerical example 1 of the invention.

FIG. 5 is a lens block diagram showing a zoom lens at the wide-angle endaccording to a numerical example 2 of the invention.

FIGS. 6A to 6D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 2 of theinvention.

FIGS. 7A to 7D are graphs showing aberration curves at the middle focallength position in the zoom lens according to the numerical example 2 ofthe invention.

FIGS. 8A to 8D are graphs showing aberration curves at the telephoto endin the zoom lens according to the numerical example 2 of the invention.

FIG. 9 is a lens block diagram showing a zoom lens at the wide-angle endaccording to a numerical example 3 of the invention.

FIGS. 10A to 10D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 3 of theinvention.

FIGS. 11A to 11D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 3 of the invention.

FIGS. 12A to 12D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 3 of theinvention.

FIG. 13 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 4 of the invention.

FIGS. 14A to 14D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 4 of theinvention.

FIGS. 15A to 15D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 4 of the invention.

FIGS. 16A to 16D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 4 of theinvention.

FIG. 17 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 5 of the invention.

FIGS. 18A to 18D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 5 of theinvention.

FIGS. 19A to 19D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 5 of the invention.

FIGS. 20A to 20D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 5 of theinvention.

FIG. 21 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 6 of the invention.

FIGS. 22A to 22D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 6 of theinvention.

FIGS. 23A to 23D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 6 of the invention.

FIGS. 24A to 24D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 6 of theinvention.

FIG. 25 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 7 of the invention.

FIGS. 26A to 26D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 7 of theinvention.

FIGS. 27A to 27D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 7 of the invention.

FIGS. 28A to 28D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 7 of theinvention.

FIG. 29 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 8 of the invention.

FIGS. 30A to 30D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 8 of theinvention.

FIGS. 31A to 31D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 8 of the invention.

FIGS. 32A to 32D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 8 of theinvention.

FIG. 33 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 9 of the invention.

FIGS. 34A to 34D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 9 of theinvention.

FIGS. 35A to 35D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 9 of the invention.

FIGS. 36A to 36D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 9 of theinvention.

FIG. 37 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 10 of the invention.

FIGS. 38A to 38D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 10 of theinvention.

FIGS. 39A to 39D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 10 of the invention.

FIGS. 40A to 40D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 10 of theinvention.

FIG. 41 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 11 of the invention.

FIGS. 42A to 42D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 11 of theinvention.

FIGS. 43A to 43D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 11 of the invention.

FIGS. 44A to 44D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 11 of theinvention.

FIG. 45 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 12 of the invention.

FIGS. 46A to 46D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 12 of theinvention.

FIGS. 47A to 47D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 12 of the invention.

FIGS. 48A to 48D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 12 of theinvention.

FIG. 49 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 13 of the invention.

FIGS. 50A to 50D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 13 of theinvention.

FIGS. 51A to 51D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 13 of the invention.

FIGS. 52A to 52D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 13 of theinvention.

FIG. 53 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 14 of the invention.

FIGS. 54A to 54D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 14 of theinvention.

FIGS. 55A to 55D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 14 of the invention.

FIGS. 56A to 56D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 14 of theinvention.

FIG. 57 is a lens block diagram showing a zoom lens at the wide-angleend according to a numerical example 15 of the invention.

FIGS. 58A to 58D are graphs showing aberration curves at the wide-angleend in the zoom lens according to the numerical example 15 of theinvention.

FIGS. 59A to 59D are graphs showing aberration curves at the middlefocal length position in the zoom lens according to the numericalexample 15 of the invention.

FIGS. 60A to 60D are graphs showing aberration curves at the telephotoend in the zoom lens according to the numerical example 15 of theinvention.

FIG. 61 is a schematic diagram showing a video camera in which a zoomlens according to the invention is used as a photographic opticalsystem.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the invention will be described indetail with reference to the drawings.

According to the embodiments of the invention, there is provided a zoomlens which satisfies at least one of the following items.

-   -   (i) To correct well astigmatism and distortion at the wide-angle        end, in particular.    -   (ii) To reduce the share of correcting aberration of a moving        lens unit while taking the smallest lens construction, and to        lessen the deterioration of performance due to the decentering        or the like of lens units caused by manufacturing errors,        thereby making it easy to manufacture the zoom lens.    -   (iii) To attain a large aperture ratio suited for a        high-density-pixel image sensor having low sensitivity.    -   (iv) To realize the good telecentric image formation on the        image side suited for a photographing system using a solid-state        image sensor while minimizing the number of constituent lens        elements of the zoom lens.    -   (v) To shorten the length on the optical axis of each lens unit        required for the barrel-retractable zoom lens, and the amount of        movement on the optical axis of each lens unit during zooming        and during focusing.    -   (vi) To correct well distortion not only at the wide-angle end        but also over the entire range of zooming.    -   (vii) To lessen the variation of the image-side telecentric        image formation due to zooming.    -   (viii) To reduce the amount of movement of a variator lens unit        while retaining the telecentric image formation, thereby        attaining the further reduction in size.    -   (ix) To simplify a focusing mechanism for a close object.

(First Embodiment)

-   -   FIG. 1 to FIGS. 20A to 20D relate to a first embodiment of the        invention, which corresponds to numerical examples 1 to 5 of the        invention to be described later.

FIG. 1 is a lens block diagram showing a zoom lens according to thenumerical example 1 of the invention. FIGS. 2A to 2D through FIGS. 4A to4D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 1 of the invention.

FIG. 5 is a lens block diagram showing a zoom lens according to thenumerical example 2 of the invention. FIGS. 6A to 6D through FIGS. 8A to8D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 2 of the invention.

FIG. 9 is a lens block diagram showing a zoom lens according to thenumerical example 3 of the invention. FIGS. 10A to 10D through FIGS. 12Ato 12D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 3 of the invention.

FIG. 13 is a lens block diagram showing a zoom lens according to thenumerical example 4 of the invention. FIGS. 14A to 14D through FIGS. 16Ato 16D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 4 of the invention.

FIG. 17 is a lens block diagram showing a zoom lens according to thenumerical example 5 of the invention. FIGS. 18A to 18D through FIGS. 20Ato 20D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 5 of the invention.

In the lens block diagrams shown in FIGS. 1, 5, 9, 13 and 17, referencecharacter L1 denotes a first lens unit of negative refractive power,reference character L2 denotes a second lens unit of positive refractivepower, reference character L3 denotes a third lens unit of positiverefractive power, reference character SP denotes an aperture stop fordetermining the brightness of an optical system, reference character IPdenotes an image plane, and reference character G denotes a glass block,such as a filter or a color separation prism.

In the basic construction of the zoom lens according to the firstembodiment, the first lens unit of negative refractive power and thesecond lens unit of positive refractive power constitute the so-calledshort zoom system, and the variation of magnification is effected bymoving the second lens unit of positive refractive power while the shiftof an image point due to the variation of magnification is compensatedfor by moving.forward and backward the first lens unit of negativerefractive power. The third lens unit of positive refractive power, whenbeing made stationary during zooming (in the case of the numericalexample 5), does not contribute to the variation of magnification, butshares the increase of a refractive power of the photographic lens dueto the reduction in size of an image sensor so as to decrease arefractive power of the short zoom system composed of the first andsecond lens units. Therefore, in particular, it is possible to suppressthe occurrence of aberrations in lens elements constituting the firstlens unit, thereby attaining good optical performance. Further, theformation of a telecentric image on the image side required for an imagepickup apparatus using a solid-state image sensor or the like isattained by making the third lens unit of positive refractive power havethe role of a field lens. On the other hand, in a case where the thirdlens unit is made to move during zooming (in the cases of the numericalexamples 1 to 4), the height from the optical axis of an off-axial rayincident on the third lens unit can be controlled. Therefore, thefaculty of correcting the various off-axial aberrations is enhanced, sothat it is possible to realize good optical performance over the entirerange of variable magnification.

Further, the stop SP is disposed on the object side of the second lensunit so as to shorten the distance between the entrance pupil and thefirst lens unit at the wide-angle end, so that the outer diameter oflens elements constituting the first lens unit is prevented fromincreasing. In addition, the various off-axial aberrations are canceledby the first lens unit and the third lens unit between which the stop SPdisposed on the object side of the second lens unit of positiverefractive power is put, so that it is possible to obtain good opticalperformance without increasing the number of constituent lens elements.

In particular, the zoom lens according to the first embodiment of theinvention has any one of the following characteristic features (1-1),(1-2) and (1-3) under the basic construction described above.

-   -   (1-1) The first lens unit includes a negative lens of meniscus        form having a concave surface facing the image side, and a        positive lens of meniscus form having a convex surface facing        the object side, and the second lens unit includes a cemented        lens A of positive refractive power as a whole disposed on the        most image side of the second lens unit and composed of a        negative lens and a positive lens, and a lens B disposed on the        most image side among lenses disposed closer to the object side        than the cemented lens A, a lens surface on the image side of        the lens B having a shape having a concave surface facing the        image side.

In addition, in the above construction (1-1), it is preferable tosatisfy at least one of the following conditions (a-1) and (a-2).

-   -   (a-1) The following conditions are satisfied:        0.5<fc/f 2<2.0  (1)        0.5<(Ra+Rb)/(Ra−Rb)<2.5  (2)        where fc is the focal length of the cemented lens A in the        second lens unit, f2 is the focal length of the second lens        unit, Ra is a radius of curvature of a lens surface on the        object side of the cemented lens A, and Rb is a radius of        curvature of the lens surface on the image side of the lens B.    -   (a-2) The second lens unit includes, in order from the object        side to the image side, a positive lens having a convex surface        facing the object side, a negative lens having a concave surface        facing the image side, and a cemented lens.    -   (1-2) The first lens unit includes a negative lens of meniscus        form having a concave surface facing the image side, and a        positive lens of meniscus form having a convex surface facing        the object side, and the second lens unit includes a negative        lens of bi-concave form, a positive lens disposed on the object        side of the negative lens of bi-concave form and having a convex        surface facing the object side, and a cemented lens of positive        refractive power as a whole disposed on the image side of the        negative lens of bi-concave form and composed of a negative lens        and a positive lens.

In addition, in the above construction (1-2), it is preferable tosatisfy at least one of the following conditions (b-1) and (b-2).

-   -   (b-1) The following conditions are satisfied:        0.3<|fn|/f 2<2.0  (3)        0<(Rd+Rc)/(Rd−Rc)<2.5  (4)        where fn is the focal length of the negative lens of bi-concave        form in the second lens unit, f2 is the focal length of the        second lens unit, Rc and Rd are radii of curvature of lens        surfaces on the object side and the image side, respectively, of        the positive lens disposed on the most object side of the second        lens unit and having a convex surface facing the object side.    -   (b-2) The third lens unit consists of one positive lens, or        consists of a cemented lens of positive refractive power as a        whole composed of a positive lens and a negative lens.    -   (1-3) The first lens unit includes a negative lens of meniscus        form having a concave surface facing the image side and a        positive lens of meniscus form having a convex surface facing        the object side, and the second lens unit includes, in order        from the object side to the image side, one or two positive        lenses, a negative lens B of bi-concave form, and a cemented        lens A composed of a negative lens and a positive lens, and the        zoom lens satisfies the following conditions:        0.5<fc/f 2<2.0  (1)        0.5<(Ra+Rb)/(Ra−Rb)<2.5  (2)        0.3<|fn|/f 2<2.0  (3)        0<(Rd+Rc)/(Rd−Rc)<2.5  (4)        where fc is the focal length of the cemented lens A in the        second lens unit, f2 is the focal length of the second lens        unit, Ra is a radius of curvature of a lens surface on the        object side of the cemented lens A, Rb is a radius of curvature        of a lens surface on the image side of the negative lens B, fn        is a focal length of the negative lens B in the second lens        unit, Rc and Rd are radii of curvature of lens surfaces on the        object side and the image side, respectively, of a positive lens        disposed on the most object side of the second lens unit and        having a convex surface facing the object side.

Next, the characteristic features of the above constructions (1-1) to(1-3) according to the first embodiment of the invention are furtherdescribed in detail.

In the zoom lens according to the first embodiment, the first lens unitof negative refractive power is composed of two lenses, i.e., in orderfrom the object side to the image side, a negative lens of meniscus formhaving a convex surface facing the object side and a positive lens ofmeniscus form having a convex surface facing the object side, or thefirst lens unit of negative refractive power is composed of threelenses, i.e., in order from the object side to the image side, a concavelens (negative lens) 11 having a concave surface facing the image side,a concave lens (negative lens) 12 having a concave surface facing theimage side and a convex lens (positive lens) 13 having a convex surfacefacing the object side. Further, the second lens unit of positiverefractive power is composed of three lens subunits including four lenselements, i.e., in order from the object side to the image side, aconvex lens (positive lens) 21 having a convex surface facing the objectside, a concave lens (negative lens) 22 of bi-concave form, and acemented lens 23 composed of a negative lens and a positive lens, or thesecond lens unit of positive refractive power is composed of four lenssubunits including five lens elements, i.e., in order from the objectside to the image side, two positive lenses, a negative lens 22 ofbi-concave form, and a cemented lens 23 composed of a negative lens anda positive lens.

Further, the third lens unit of positive refractive power is composed ofone convex lens or a cemented lens composed of a positive lens and anegative lens. By adopting such a desired refractive power arrangementas to be compatible with the correction of aberrations, as describedabove, it is possible to attain the compactness of a lens system whilekeeping good optical performance.

The first lens unit of negative refractive power has the role of causingan off-axial principal ray to be pupil-imaged on the center of the stop.In particular, since the amount of refraction of the off-axial principalray is large at the wide-angle end, the various off-axial aberrations,particularly, astigmatism and distortion, tend to occur. Therefore,similarly to the ordinary. wide-angle lens, the zoom lens according tothe first embodiment is made to have the concave-convex arrangement bywhich the increase of the lens diameter on the most object side can beprevented, and then the negative refractive power is shared by the twonegative lens units 11 and 12 which mainly share the negative refractivepower of the first lens unit. Lenses constituting the first lens unithave respective shapes close to concentrical spherical surfaces centeredon the center of the stop so as to suppress the occurrence of off-axialaberration caused by the refraction of an off-axial principal ray. Thus,each of the negative lenses 11 and 12 is made in the meniscus formhaving a concave surface facing the image side, and the positive lens 13is made in the meniscus form having a convex surface facing the objectside.

The second lens unit of positive refractive power is constructed in asymmetrical form on the refractive power arrangement by respectivelydisposing positive lenses before and behind the concave lens 22 ofbi-concave form. This is because, since the second lens unit is arrangedto move greatly during the variation of magnification, in order toprevent the degradation of optical performance due to the decentering orthe like of lens units caused by a manufacturing error, it is necessaryfor the second lens unit itself to remove spherical aberration, coma,etc., to a certain degree.

The convex lens 21 disposed on the most object side of the second lensunit is made in a form convex toward the object side so as to prevent anoff-axial principal ray having exited from the first lens unit frombeing greatly refracted to generate the various off-axial aberrations.Further, also, in order to decrease the amount of occurrence ofspherical aberration with respect to an on-axial light flux havingexited from the first lens unit in a diverging manner, the convex lens21 is made in a form convex toward the object side.

Further, both lens surfaces on the object side and the image side of theconcave lens 22 are concave, and a negative air lens is formed by theconcave lens 22 and each of the convex lens 21 and the positive cementedlens 23 which are disposed before and behind the concave lens 22, sothat spherical aberration and coma which occur owing to the largeaperture ratio are corrected well.

Further, the cemented lens 23 is disposed on the image side of theconcave lens 22 to correct chromatic aberration well. In the zoom lensaccording to the first embodiment, since the height at which anoff-axial light flux bends in the first lens unit is high at thewide-angle end and low at the telephoto end, the variation of lateralchromatic aberration due to the variation of magnification occurs in thefirst lens unit in particular. Therefore, the refractive powerarrangement of the first lens unit and the selection of glass materialtherefor are made in such a way as to make, especially, the variation oflateral chromatic aberration minimum. In a case where the first lensunit is formed in the concave-convex construction, as described above,to make the first lens unit compact and the number of constituent lenselements of the first lens unit is made to be two or three, a componentof the variation of longitudinal chromatic aberration tends to. remainwithin the first lens unit. Therefore, the cemented lens is disposedwithin the second lens unit to correct longitudinal chromatic aberrationwell.

Further, in order to cause the second lens unit also to take its shareof the correction of lateral chromatic aberration even to a smallextent, it is effective that the cemented lens is disposed distant fromthe stop. Therefore, in the first embodiment, the cemented lens isdisposed on the image side of the concave lens 22.

The third lens unit of positive refractive power is constructed with aconvex lens of form having a convex surface facing the object side, oris constructed with a cemented lens composed of a positive lens and anegative lens, thereby making the image side of the third lens unittelecentric. In addition, the third lens unit is made to serve also as afield lens.

Further, in order to attain the further improvement of opticalperformance while constructing each lens unit with a less number ofconstituent lens elements, an aspheric surface is effectively introducedinto the zoom lens according to the first embodiment.

In the case of the numerical example 1 shown in FIG. 1, a lens surfaceon the image side of the-concave lens 11 of the first lens unit is madeto be an aspheric surface of such a shape that a diverging functionbecomes progressively weaker toward the marginal portion thereof,thereby correcting curvature of field, astigmatism and distortion,especially, at the wide-angle side to lower the variation of aberrationdue to the variation of magnification.

Further, a lens surface on the object side of the convex lens 21 of thesecond lens unit is made to be an aspheric surface of such a shape thata converging function becomes progressively weaker toward the marginalportion thereof, thereby effectively correcting spherical aberration,which becomes conspicuous owing to the large aperture ratio.

Further, a lens surface on the object side of the convex lens 31 of thethird lens unit is made to be an aspheric surface of such a shape that aconverging function becomes progressively weaker toward the marginalportion thereof, thereby effectively correcting curvature of field,astigmatism and distortion in the whole range of the variation ofmagnification.

In a case where a near-distance object is photographed by using the zoomlens according to the first embodiment, good focusing performance can beobtained by moving the first lens unit toward the object side. However,the rear-focusing method in which the third lens unit is moved towardthe object side for focusing may be employed. This method gives theadvantage of preventing the diameter of a front lens member fromincreasing due to focusing, the advantage of shortening the minimumimaging distance, and the advantage of lightening the focusing lensunit.

Next, the technical significance of each of the above-mentionedconditions (1) to (4) is described.

The condition (1) is an inequality for regulating the refractive powerof the cemented lens of the second lens unit. The second lens unit inthe first embodiment takes the symmetrical refractive power arrangementof positive, negative and positive refractive powers, as mentioned inthe foregoing. The refractive power of the cemented lens bears thepositive refractive power on the image side of the second lens unit.Therefore, it is desirable that the refractive power of the cementedlens lies within a certain range compared with the refractive power ofthe second lens unit.

If the refractive power of the cemented lens becomes weaker beyond theupper limit of the condition (1), it becomes necessary to strengthen therefractive power of the positive lens on the object side of the secondlens unit to make the second lens unit have a necessary convergingfunction. In this instance, excessive spherical aberration occurs, thecorrection of which would become insufficient even if an asphericsurface is used. If the refractive power of the positive lens on theobject side of the second lens unit is not strengthened, the refractivepower of the second lens unit itself becomes weaker. Therefore, theamount of movement for the variation of magnification becomes large,causing an increase of the total lens length and the diameter of a frontlens member, so that it becomes impossible to construct a compact zoomlens. on the other hand, if the refractive power of the cemented lensbecomes stronger beyond the lower limit of the condition (1), thePetzval sum in the second lens unit becomes large in the positivedirection, causing curvature of field in the under direction. Further,in order to correct longitudinal chromatic aberration, it is necessaryto make the curvature of the cementing surface of the cemented lensstronger. Accordingly, in order to secure the edge thickness of thepositive lens of the cemented lens, the lens thickness at the centralportion of the cemented lens has to be made larger. This isdisadvantageous in compactness of the zoom lens.

The condition (2) is an inequality for defining the shape factor of anair lens of negative refractive power which is formed by the cementedlens disposed on the image side of the second lens unit and the concavelens disposed immediately before the cemented lens.

If the stop is disposed on the object side of the second lens unit, comaof the same sign is caused by a lens surface on the object side of thepositive lens disposed on the object side of the second lens unit and alens surface on the object side of the concave lens of the second lensunit. On the other hand, coma of the sign different from the above signis caused by a lens surface on the object side of the air lens, and comaof the same sign as the above sign is caused by a lens surface on theimage side of the air lens. Therefore, if the curvature of the lenssurface on the object side of the air lens is made strong to a certainextent in the form of a concave surface facing the image side and, onthe other hand, the curvature of the lens surface on the image side ofthe air lens is made relatively weak, coma is effectively corrected.Incidentally, when the shape factor in the condition (2) is larger than“1”, the air lens takes the meniscus form, and, when smaller than “1”,the air lens is a bi-convex lens. As the shape factor becomes largerfrom “1”, the lens surface on the image side of the air lens has asmaller radius of curvature while having the center of curvature thereofon the image side, and, on the other hand, as the shape factor becomessmaller from “1”, the lens surface on the image side of the air lens hasa smaller radius of curvature while having the center of curvaturethereof on the object side.

If the degree of meniscus form of the air lens is strengthened beyondthe upper limit of the condition (2), the curvature of the lens surfaceon the image side of the air lens becomes too strong, so that thefaculty of the air lens for correcting coma becomes weak. As a result,coma is insufficiently corrected by the second lens unit.

If the shape factor of the air lens becomes smaller than “1”, the lenssurface on the image side of the air lens has the center of curvaturethereof on the object side, so that the air lens takes the bi-convexform. Accordingly, the cemented lens, which is disposed on the imageside of the air lens, takes the meniscus form. Then, in order to makethe cemented lens have such a refractive power as to satisfy thecondition (1), it is necessary to strengthen the curvature of the lenssurface on the image side of the cemented lens. If the lower limit ofthe condition (2) is exceeded, as a result, the curvature of the lenssurface on the image side of the cemented lens becomes too strong, sothat spherical aberration in the under direction occurs, which is notsufficiently corrected even by using an aspheric surface.

The condition (3) is an inequality for regulating a refractive power ofthe negative lens of bi-concave form of the second lens unit.

If the refractive power of the negative lens becomes weak beyond theupper limit of the condition (3), the Petzval sum in the second lensunit increases in the positive direction, thereby causing curvature offield in the under direction. Further, it becomes impossible to secure asufficient back focal distance for disposing a filter or the like.Furthermore, a problem arises in that it is impossible to make the exitpupil sufficiently distant from the image plane.

If the refractive power of the negative lens becomes strong beyond thelower limit of the condition (3), spherical aberration isover-corrected, curvature of field occurs in the over direction, and theback focal distance becomes too long to make the zoom lens compact.

The condition (4) is an inequality for defining the shape factor of thepositive lens on the object side of the second lens unit.

If the curvature of the lens surface on the image side of the positivelens becomes strong while having the center of curvature thereof on theimage side beyond the upper limit of the condition (4), in particular,coma occurs conspicuously, which is difficult to correct even by usingan aspheric surface.

If the curvature of the lens surface on the image side of the positivelens becomes strong while having the center of curvature thereof on theobject side beyond the lower limit of the condition (4), the angle ofincidence of an on-axial land ray on the lens surface on the image sideof the positive lens becomes too large, so that spherical aberrationoccurs in the under direction.

Next, numerical data of the numerical examples 1 to 5 of the inventionare shown. In the numerical data of the numerical examples 1 to 5, Ridenotes the radius of curvature of the i-th surface, when counted fromthe object side, Di denotes the lens thickness or air separation betweenthe i-th surface and the (i+1)th surface, when counted from the objectside, Ni and vi respectively denote the refractive index and Abbenumber, relative to d-line, of the i-th optical member, when countedfrom the object side. Further, the two surfaces closest to the imageside constitute a filter member, such as a crystal low-pass filter or aninfrared cutting filter.

The shape of an aspheric surface is expressed in the coordinates with anX axis in the optical axis direction and an H axis in the directionperpendicular to the optical axis, the direction in which light advancesbeing taken as positive, by the following equation:$X = {\frac{\left( {1/R} \right)H^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)\left( {H\text{/}R} \right)^{2}}}} + {BH}^{4} + {CH}^{6} + {DH}^{8} + {EH}^{~10} + {FH}^{12}}$where R is the radius of osculating sphere, and K, B, C, D, E and F areaspheric coefficients. Further, the indication “e−0X” means “×10^(−X)”.

In addition, the values of the factors in the above-mentioned conditions(1) to (4) for the numerical examples 1 to 5 are listed in Table-1.

[Numerical Example 1]

The zoom lens according to the numerical example 1 is constructed with,in order from the object side to the image side, a first lens unit ofnegative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side. Lens data of the numerical example 1 isshown as follows. f = 1.00-1.99 Fno = 2.90-4.12 2ω = 68.6°-36.8° R1 =7.468 D1 = 0.21 N1 = 1.674700 ν1 = 54.9 R2 = 0.993* D2 = 0.21 R3 = 2.407D3 = 0.10 N2 = 1.728250 ν2 = 28.5 R4 = 1.188 D4 = 0.19 R5 = 1.486 D5 =0.32 N3 = 1.846660 ν3 = 23.8 R6 = 5.074 D6 = Variable R7 = Stop D7 =0.00 R8 = 0.981* D8 = 0.38 N4 = 1.693500 ν4 = 53.2 R9 = −4.331 D9 = 0.04R10 = −1.864 D10 = 0.14 N5 = 1.516330 ν5 = 64.1 R11 = 0.906 D11 = 0.13R12 = 17.071 D12 = 0.08 N6 = 1.846660 ν6 = 23.8 R13 = 0.966 D13 = 0.35N7 = 1.772499 ν7 = 49.6 R14 = −1.646 D14 = Variable R15 = 2.410* D15 =0.25 N8 = 1.583130 ν8 = 59.5 R16 = −38.921 D16 = Variable R17 = ∞ D17 =0.43 N9 = 1.544270 ν9 = 70.6 R18 = ∞ Variable Focal Length Separation1.00 1.50 1.99 D6 1.88 0.80 0.41 D14 0.77 1.43 2.34 D16 0.60 0.58 0.32Aspheric Coefficients: R2 K = 0 B = −1.23832e−01 C = −2.29538e−02 D =−2.45611e−01 E = 3.31822e−01 F = −2.96505e−01 R8 K = 0 B = −5.79780e−02C = −1.08652e−02 D = 2.34725e−02 E = 2.63031e−01 F = 0.00000e+00 R15 K =0 B = 5.91674e−04 C = −5.06821e−02 D = 2.87149e−01 E = −5.94448e−01 F =4.55368e−01*Aspheric Surface[Numerical Example 2]

The zoom lens according to the numerical example 2 is constructed with,in order from the object side to the image side, a first lens unit ofnegative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side. Lens data of the numerical example 2 isshown as follows. f = 1.00-2.54 Fno = 2.89-4.60 2ω = 70.2°-28.0° R1 =7.492 D1 = 0.21 N1 = 1.674700 ν1 = 54.9 R2 = 1.121* D2 = 0.30 R3 =−7.375 D3 = 0.13 N2 = 1.720000 ν2 = 43.7 R4 = 3.048 D4 = 0.19 R5 = 2.496D5 = 0.27 N3 = 1.846660 ν3 = 23.8 R6 = 13.429 D6 = Variable R7 = Stop D7= 0.00 R8 = 1.142* D8 = 0.32 N4 = 1.693500 ν4 = 53.2 R9 = −21.428 D9 =0.03 R10 = −3.947 D10 = 0.22 N5 = 1.517417 ν5 = 52.4 R11 = 1.061 D11 =0.08 R12 = 2.860 D12 = 0.08 N6 = 1.846660 ν6 = 23.8 R13 = 1.004 D13 =0.32 N7 = 1.772499 ν7 = 49.6 R14 = −2.683 D14 = Variable R15 = 2.498*D15 = 0.29 N8 = 1.583130 ν8 = 59.5 R16 = −31.782 D16 = Variable R17 = ∞D17 = 0.43 N9 = 1.544270 ν9 = 70.6 R18 = ∞ Variable Focal LengthSeparation 1.00 1.76 2.54 D6 2.04 0.77 0.25 D14 1.69 2.69 3.68 D16 0.260.21 0.16 Aspheric Coefficients: R2 K = 0 B = −3.92457e−02 C =1.76441e−02 D = −1.79210e−01 E = 3.23743e−01 F = −2.57814e−01 R8 K = 0 B= −4.52188e−02 C = −7.37087e−03 D = 0.00000e+00 E = 0.00000e+00 F =0.00000e+00 R15 K = 0 B = −1.06457e−01 C = 2.32651e−01 D = −1.16441e+00E = 2.17741e+00 F = −1.56135e+00*Aspheric Surface[Numerical Example 3]

The zoom lens according to the numerical example 3 is constructed with,in order from the object side to the image side, a first lens unit ofnegative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side.

The numerical example 3 differs from the numerical example 1 in that thenumber of constituent lens elements of the first lens unit is two. Inthe numerical example 3, the first lens unit is constructed with anegative lens of meniscus form having a concave surface facing the imageside and a positive lens of meniscus form having a convex surface facingthe object side, that is, two concave lenses in the numerical example 1are formed into one concave lens. This arrangement gives such advantagesthat the number of lens elements is reduced to lead to reduction incost, and the front lens member is reduced in weight. Lens data of thenumerical example 3 is shown as follows. f = 1.00-2.00 Fno = 2.49-3.502ω = 70.2°-37.6° R1 = 15.872 D1 = 0.21 N1 = 1.674700 ν1 = 54.9 R2 =0.984* D2 = 0.51 R3 = 2.011 D3 = 0.25 N2 = 1.846660 ν2 = 23.8 R4 = 3.882D4 = Variable R5 = Stop D5 = 0.00 R6 = 1.049* D6 = 0.38 N3 = 1.693500 ν3= 53.2 R7 = −18.496 D7 = 0.06 R8 = −1.875 D8 = 0.14 N4 = 1.522494 ν4 =59.8 R9 = 1.019 D9 = 0.10 R10 = 7.075 D10 = 0.08 N5 = 1.805181 ν5 = 25.4R11 = 0.879 D11 = 0.35 N6 = 1.772499 ν6 = 49.6 R12 = −1.696 D12 =Variable R13 = 2.412* D13 = 0.25 N7 = 1.583130 ν7 = 59.5 R14 = −39.003D14 = Variable R15 = ∞ D15 = 0.43 N8 = 1.544270 ν8 = 70.6 R16 = ∞Variable Focal Length Separation 1.00 1.52 2.00 D4 2.12 0.84 0.41 D120.79 1.45 2.35 D14 0.59 0.57 0.32 Aspheric Coefficients: R2 K = 0 B =−1.14032e−01 C = 2.67387e−02 D = −3.23821e−01 E = 4.20448e−01 F =−3.39683e−01 R6 K = 0 B = −3.07051e−02 C = 2.68063e−02 D = 0.00000e+00 E= 0.00000e+00 F = 0.00000e+00 R13 K = 0 B = −2.75565e−02 C = 1.56521e−01D = −5.60681e−01 E = 1.06327e+00 F = −7.73626e−01*Aspheric Surface[Numerical Example 4]

The zoom lens according to the numerical example 4 is constructed with,in order from the object side to the image side, a first lens unit ofnegative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side.

The numerical example 4 differs from the numerical example 1 in that thenumber of constituent lens elements of the second lens unit is five,being grouped into four lens subunits. In the numerical example 4, thesecond lens unit is constructed with, in order from the object side tothe image side, a positive lens of meniscus form having a convex surfacefacing the object side, a convex lens of bi-convex form, a concave lensof bi-concave form, and a cemented lens of positive refractive power asa whole composed of a concave lens and a convex lens, that is, onepositive lens on the object side in the numerical example 1 is formedinto two positive lenses. This arrangement enables the two positivelenses to share the function of converging an on-axial light flux whichhas exited from the first lens unit in a diverging state, and,therefore, gives such advantages that it is possible to reduce theoccurrence of spherical aberration and it is possible to construct aphotographic lens having a larger aperture diameter. Lens data of thenumerical example 4 is shown as follows. f = 1.00-2.00 Fno = 2.00-3.002ω = 66.0°-35.2° R1 = 7.477 D1 = 0.21 N1 = 1.674700 ν1 = 54.9 R2 =1.046* D2 = 0.20 R3 = 2.556 D3 = 0.10 N2 = 1.728250 ν2 = 28.5 R4 = 1.145D4 = 0.19 R5 = 1.463 D5 = 0.27 N3 = 1.846660 ν3 = 23.8 R6 = 4.613 D6 =Variable R7 = Stop D7 = 0.00 R8 = 1.381 D8 = 0.25 N4 = 1.693500 ν4 =53.2 R9 = 6.370 D9 = 0.03 R10 = 1.615* D10 = 0.29 N5 = 1.693500 ν5 =53.2 R11 = −4.778 D11 = 0.04 R12 = −2.130 D12 = 0.14 N6 = 1.516330 ν6 =64.1 R13 = 0.907 D13 = 0.14 R14 = −70.592 D14 = 0.08 N7 = 1.846660 ν7 =23.8 R15 = 0.990 D15 = 0.35 N8 = 1.772499 ν8 = 49.6 R16 = −1.991 D16 =Variable R17 = 1.819* D17 = 0.29 N9 = 1.583130 ν9 = 59.5 R18 = −38.968D18 = Variable R19 = ∞ D19 = 0.43 N10 = 1.544270 ν10 = 70.6 R20 = ∞Variable Focal Length Separation 1.00 1.49 2.00 D6 1.88 0.92 0.41 D160.91 1.59 2.26 D18 0.39 0.35 0.32 Aspheric Coefficients: R2 K = 0 B =−1.13188e−01 C = 1.50616e−04 D = −2.51746e−01 E = 3.47476e−01 F =−2.63121e−01 R10 K = 0 B = −2.71823e−02 C = 2.14414e−02 D = −2.52640e−02E = 0.00000e+00 F = 0.00000e+00 R17 K = 0 B = −3.50857e−02 C =3.08965e−02 D = 1.84237e−01 E = −6.40556e−01 F = 5.97621e−01*Aspheric Surface[Numerical Example 5]

The zoom lens according to the numerical example 5 is constructed with,in order from the object side to the image side, a first lens unit ofnegative refractive power, a second lens unit of positive refractivepower, and a third lens unit of positive refractive power. Duringzooming from the wide-angle end to the telephoto end, the first lensunit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitremains stationary.

The numerical example 5 differs from the numerical example 1 in that thenumber of constituent lens elements of the third lens unit is two, beinggrouped into one lens subunit. In the numerical example 5, the thirdlens unit is constructed with a cemented lens of positive refractivepower as a whole composed of a convex lens and a concave lens, that is,a single lens in the numerical example 1 is formed into a cemented lens.This arrangement enables lateral chromatic aberration, in particular, tobe corrected by the third lens unit. As mentioned in the foregoing, thevariation of lateral chromatic aberration due to zooming is causedgreatly by the first lens unit. However, in the case of the numericalexample 5, the correction of lateral chromatic aberration can be sharedsuch that the component of the variation of lateral chromatic aberrationis corrected by the first lens unit and the absolute amount of lateralchromatic aberration is corrected by the third lens unit. Accordingly,the numerical example 5 has such advantages that it is possible tocorrect lateral chromatic aberration well over the whole range of thevariation of magnification even when the zoom ratio is increased.

Further, the numerical example 5 differs from the numerical example 1 inthat the third lens unit remains stationary during zooming. With thethird lens unit kept stationary, the numerical example 5 has suchadvantages that, since any moving mechanism for the third lens unit isnot necessary, the construction of a lens barrel can be simplified. Lensdata of the numerical example 5 is shown as follows. f = 1.00-2.98 Fno =2.78-4.60 2ω = 70.0-23.8° R1 = 7.471 D1 = 0.21 N1 = 1.674700 ν1 = 54.9R2 = 1.392* D2 = 0.29 R3 = −8.099 D3 = 0.13 N2 = 1.723420 ν2 = 38.0 R4 =1.731 D4 = 0.19 R5 = 2.191 D5 = 0.32 N3 = 1.846660 ν3 = 23.8 R6 =137.077 D6 = Variable R7 = Stop D7 = 0.00 R8 = 1.335* D8 = 0.38 N4 =1.693500 ν4 = 53.2 R9 = −5.330 D9 = 0.05 R10 = −2.015 D10 = 0.14 N5 =1.517417 ν5 = 52.4 R11 = 1.319 D11 = 0.08 R12 = 7.466 D12 = 0.08 N6 =1.846660 ν6 = 23.8 R13 = 1.351 D13 = 0.35 N7 = 1.772499 ν7 = 49.6 R14 =−1.958 D14 = Variable R15 = 2.272* D15 = 0.27 N8 = 1.583130 ν8 = 59.5R16 = −7.923 D16 = 0.08 N9 = 1.698947 ν9 = 30.1 R17 = −31.691 D17 = 0.08R18 = ∞ D18 = 0.43 N10 = 1.544270 ν10 = 70.6 R19 = ∞ Variable FocalLength Separation 1.00 1.99 2.98 D6 2.92 0.92 0.25 D14 2.17 3.41 4.64Aspheric Coefficients: R2 K = 0 B = −3.90048e−02 C = 8.55478e−02 D =−3.52446e−01 E = 5.28091e−01 F = −2.97792e−01 R8 K = 0 B = −2.41197e−02C = 1.74507e−02 D = 0.00000e+00 E = 0.00000e+00 F = 0.00000e+00 R15 K =0 B = −5.30968e−02 C = −9.80294e−02 D = 1.70223e−01 E = −2.85852e−01 F =1.85253e−01*Aspheric Surface

According to the first embodiment of the invention, it is possible toattain a zoom lens which is suited for a photographic system using asolid-state image sensor, has a high variable magnification ratiodespite being compact and small in diameter with less constituent lenselements, is corrected particularly for chromatic aberration, and hasexcellent optical performance.

(Second Embodiment)

FIG. 21 to FIGS. 32A to 32D relate to a second embodiment of theinvention, which corresponds to numerical examples 6 to 8 of theinvention to be described later.

FIG. 21 is a lens block diagram showing a zoom lens according to thenumerical example 6 of the invention. FIGS. 22A to 22D through FIGS. 24Ato 24D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 6 of the invention.

FIG. 25 is a lens block diagram showing a zoom lens according to thenumerical example 7 of the invention. FIGS. 26A to 26D through FIGS. 28Ato 28D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 7 of the invention.

FIG. 29 is a lens block diagram showing a zoom lens according to thenumerical example 8 of the invention. FIGS. 30A to 30D through FIGS. 32Ato 32D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 8 of the invention.

In the lens block diagrams shown in FIGS. 21, 25 and 29, referencecharacter L1 denotes a first lens unit of negative refractive power,reference character L2 denotes a second lens unit of positive refractivepower, reference character L3 denotes a third lens unit of positiverefractive power, reference character SP denotes an aperture stop fordetermining the rightness of an optical system, reference character IPdenotes an image plane, and reference character G denotes a glass block,such as a filter or a color separation prism.

The zoom lens according to the second embodiment has three lens units,i.e., in order from the object side to the image side, the first lensunit L1 of negative refractive power, the second lens unit L2 ofpositive refractive power and the third lens unit L3 of positiverefractive power. During zooming from the wide-angle end to thetelephoto end, the first lens unit makes a reciprocating motion convextoward the image side, the second lens unit moves toward the objectside, and the third lens unit moves toward the image side or moves witha locus convex toward the image side.

In the zoom lens according to the second embodiment, the variation ofmagnification is effected mainly by moving the second lens unit whilethe shift of an image point due to the variation of magnification iscompensated for by moving forward and backward the first lens unit andmoving the third lens unit toward the image side or moving the thirdlens unit with a locus convex toward the image side.

The third lens unit shares the increase of a refractive power of thephotographic lens due to the reduction in size of the image sensor,thereby reducing a refractive power of the short zoom system composed ofthe first and second lens units, so that the occurrence of aberration bylenses constituting the first lens unit can be suppressed, so as toattain high optical performance. Further, the telecentric imageformation on the image side necessary for the photographing apparatus(optical apparatus) using the image sensor or the like is attained bygiving the third lens unit the roll of a field lens.

Further, the stop SP is disposed on the most object side of the secondlens unit, thereby shortening the distance between the entrance pupiland the first lens unit on the wide-angle side, so that the increase ofthe diameter of lenses constituting the first lens unit can beprevented. In addition, the various off-axial aberrations are canceledby the first lens unit and the third lens unit across the stop disposedon the object side of the second lens unit, so that good opticalperformance can be obtained without increasing the number of constituentlenses.

The zoom lens according to the second embodiment is characterized inthat the first lens unit has one negative lens and one positive lens,the second lens unit is composed of one cemented lens and a positivelens, and the third lens unit is has at least one positive lens.

As has been described in the foregoing, according to the secondembodiment, the first lens unit of negative refractive power is composedof two lenses, i.e., in order from the object side to the image side, anegative lens 11 having a concave surface facing the image side, and apositive lens 12 of meniscus form having a convex surface facing theobject side, the second lens unit of positive refractive power iscomposed of three lenses as a whole, i.e., a positive lens 21 ofbi-convex form, a negative lens 22 having a concave surface facing theobject side, and a positive lens 23 of bi-convex form, two of the threelenses constituting a cemented lens, and the third lens unit of positiverefractive power is composed of a single positive lens 31 having aconvex surface facing the object side.

With the respective lens units having such a lens construction as tomake the desired refractive power arrangement and the correction ofaberration compatible with each other, as described above, it ispossible to attain the compactness of a lens system while keeping thegood optical performance of the lens system. The first-lens unit ofnegative refractive power has the role of causing an off-axial principalray to be pupil-imaged on the center of a stop, and, particularly, onthe wide-angle side, the amount of refraction of an off-axial principalray is large. Therefore, in the first lens unit, the various off-axialaberrations, particularly, astigmatism and distortion, are apt to occur.Accordingly, similarly to an ordinary wide-angle lens, the first lensunit is made to have the construction having a negative lens and apositive lens so as to prevent the diameter of a lens disposed on themost object side from increasing. Further, it is preferable that a lenssurface on the image side of the negative lens 11 is such an asphericsurface that a negative refractive power becomes progressively weakertoward a marginal portion of the lens surface. By this arrangement,astigmatism and distortion are corrected in a well-balanced manner, andthe first lens unit is composed of such a small number of lenses as two,so that it becomes easy to make the entire lens system compact. Inaddition, in order to prevent the occurrence of an off-axial aberrationdue to the refraction of an off-axial principal ray, each of lensesconstituting the first lens unit has a lens surface approximate toconcentric spherical surfaces having the center on a point at which thestop and the optical axis intersect.

The second lens unit of positive refractive power has the positive lens21 of bi-convex form disposed on the most object side of the second lensunit, so that the second lens unit has such a shape as to lessen theangle of refraction of an off-axial principal ray having exited from thefirst lens unit, thereby preventing the various off-axial aberrationsfrom occurring. Further, the positive lens 21 is a lens arranged toallow an on-axial ray to pass at the largest height, and is concernedwith the correction of, mainly, spherical aberration and coma. In thesecond embodiment, it is preferable that a lens surface on the objectside of the positive lens 21 is such an aspheric surface that a positiverefractive power becomes progressively weaker toward a marginal portionof the lens surface. By this arrangement, it becomes easy to correctwell spherical aberration and coma.

In the zoom lens according to the numerical example 6 shown in FIG. 21,the negative lens 22 disposed on the image side of the positive lens 21is made to have a concave surface facing the object side, so that anegative air lens is formed by the lens surface on the image side of thepositive lens 21 and the concave surface on the object side of thenegative lens 22. Accordingly, it is possible to correct sphericalaberration occurring due to the increase of an aperture ratio.

Further, in the zoom lenses according to the numerical examples 6 and 7shown in FIGS. 21 and 25, it is preferable that a lens surface on theimage side of the positive lens 23 disposed on the most image side ofthe second lens unit L2 is such an aspheric surface that a positiverefractive power becomes progressively stronger toward a marginalportion of the lens surface. By this arrangement, it is possible toeffectively correct spherical aberration, which becomes conspicuous dueto the increase of an aperture ratio.

In addition, in the second embodiment, in order to cope with thereduction of the amount of chromatic aberration, which is requiredaccording to the increased number of pixels and the minimization of cellpitches of a solid-state image sensor such as a CCD, a cemented lenscomposed of a negative lens and a positive lens cemented together isdisposed in the second lens unit. By this arrangement, it is possible tocorrect well longitudinal chromatic aberration and lateral chromaticaberration.

The third lens unit of positive refractive power has a convex lens(positive lens) 31 having a convex surface facing the object side, andserves also as a field lens for making the zoom lens telecentric on theimage side. Further, a lens surface on the image side of the convex lens31 is such an aspheric surface that a positive refractive power becomesprogressively weaker toward a marginal portion of the lens surface, andcontributes to the correction of the various off-axial aberrations overthe entire zooming range. Now, when the back focal distance is denotedby sk′, the focal length of the third lens unit is denoted by f3, andthe image magnification of the third lens unit is denoted by β3, thefollowing relation is obtained:sk′=f 3(1−β3)provided that 0<β3<1.0. Here, when the third lens unit is moved towardthe image side during the variation of magnification from the wide-angleend to the telephoto end, the back focal distance sk′ decreases, so thatthe image magnification β3 of the third lens unit increases on thetelephoto side. Then, as a result, the third lens unit shares thevariation of magnification with the second lens unit, so that the amountof movement of the second lens unit is reduced. Therefore, since such aspace for the movement of the second lens unit can be saved, the thirdlens unit contributes to the reduction in size of the lens system.

When a close-distance object is to be photographed by using the zoomlens according to the second embodiment, the good optical performancecan be obtained by moving the first lens unit toward the object side.However, it is preferable to move the third lens unit also toward theobject side. This arrangement prevents the increase of the diameter of afront lens member due to the focusing movement of the first lens unitwhich is disposed on the most object side, prevents the increase of theload on an actuator for moving the first lens unit which is the heaviestamong the lens units, and makes it possible to move, during zooming, thefirst lens unit and the second lens unit in an interlocking relationsimply with a cam or the like used. Therefore, it is possible to attainthe simplification of a mechanism and the enhancement of precisionthereof.

Further, in a case where focusing is performed by using the third lensunit, if the third lens unit is arranged to be moved toward the imageside during the variation of magnification from the wide-angle end tothe telephoto end, the telephoto end, at which the amount of movementfor focusing is large, can be located on the image side. Accordingly, itbecomes possible to minimize the amount of total movement of the thirdlens unit required for zooming and focusing. This arrangement makes itpossible to attain the compactness of the entire lens system.

Further, according to the second embodiment, it is more preferable tosatisfy at least one of the following conditions (c-1) to (c-4).

-   -   (c-1) The following conditions are satisfied:        nd<1.8  (5)        vd<40  (6)        where nd and vd are a refractive index and Abbe number,        respectively, of material of the negative lens included in the        second lens unit.

If the upper limit of the condition (5) is exceeded, the Petzval sumincreases in the positive direction, so that it becomes difficult tocorrect curvature of field. If the upper limit of the condition (6) isexceeded, it becomes disadvantageously difficult to correct longitudinalchromatic aberration at the telephoto end.

-   -   (c-2) The following condition is satisfied:        0.1<|X 1/X 3|<7.0  (7)        where X1 is a distance on the optical axis between a position at        which the first lens unit is located on the most object side and        a position at which the first lens unit is located on the most        image side during the variation of magnification from the        wide-angle end to the telephoto end, and X3 is a distance on the        optical axis between a position at which the third lens unit is        located on the most object side and a position at which the        third lens unit is located on the most image side during the        variation of magnification from the wide-angle end to the        telephoto end when an object distance is infinity.

The condition (7) is provided for shortening the total length of theoptical system and for shortening the total length of the entire lenssystem obtained when the lens system is retracted.

Here, the distance X1 is the total stroke of the first lens unit duringthe variation of magnification from the wide-angle end to the telephotoend, and the distance X3 is the total stroke of the third lens unitduring the variation of magnification from the wide-angle end to thetelephoto end when an object distance is infinity.

If the lower limit of the condition (7) is exceeded, the amount ofmovement of the third lens unit on the optical axis increases, and itbecomes necessary to lengthen the motor shaft for moving the third lensunit, so that it becomes disadvantageously difficult to shorten thetotal length of the lens system as retracted. If the upper limit of thecondition (7) is exceeded, the locus of the first lens unit convextoward the image side becomes sharp, and the angle of a cam locus forthe first lens unit leading from the wide-angle end to the telephoto endbecomes large, so that the total length of the lens system as retractedis caused to become large disadvantageously.

-   -   (c-3) The following condition is satisfied:        0.25<(DL 1 +DL 2+DL 3)/DL<0.45  (8)        where DL is a distance, at the telephoto end, from a vertex on        the object side of a lens disposed on the most object side of        the first lens unit to an image plane, DL1 is a distance from        the vertex on the object side of the lens disposed on the most        object side of the first lens unit to a vertex on the image side        of a lens disposed on the most image side of the first lens        unit, DL2 is a distance from a vertex on the object side of a        lens disposed on the most object side of the second lens unit to        a vertex on the image side of a lens disposed on the most image        side of the second lens unit, and DL3 is a distance from a        vertex on the object side of a lens disposed on the most object        side of the third lens unit to a vertex on the image side of a        lens disposed on the most image side of the third lens unit.

The condition (8) is provided for shortening the total length of theoptical system and for shortening the total length of the entire lenssystem obtained when the lens system is retracted.

If the upper limit of the condition (8) is exceeded, although the totallength of the optical system at the telephoto end becomes short, the sumof lengths of the respective lens units on the optical axis becomeslarge, so that the total length of the entire lens system as retractedbecomes long disadvantageously. If the lower limit of the condition (8)is exceeded, although the sum of lengths of the respective lens units onthe optical axis becomes small, the total length of the optical systemat the telephoto end becomes long, and the amount of movement of eachlens unit is necessarily increased. Therefore, the length of a cam ringor the like for moving each lens unit becomes long, and, as a result,the total length of the entire lens system as retracted does not becomeshort.

-   -   (c-4) The following condition is satisfied:        0.02<DA 2/DD 2<0.25  (9)        where DD2 is the sum of thicknesses on the optical axis of        lenses constituting the second lens unit, and DA2 is the sum of        air separations included in the second lens unit.

The condition (9) is provided for making the compactness of the opticalsystem and the attainment of good optical performance compatible witheach other.

If the upper limit of the condition (9) is exceeded, the length of thesecond lens unit on the optical axis becomes long, so that it becomesdisadvantageously difficult to attain the compactness of the opticalsystem. If the lower limit of the condition (9) is exceeded, the powerof the air lens becomes small, so that it becomes disadvantageouslydifficult to correct spherical aberration.

Next, the concrete lens construction of each of the zoom lensesaccording to the numerical examples 6 to 8 is described.

[Numerical Example 6]

The zoom lens according to the numerical example 6 is a zoom lens havingthe variable magnification ratio of about 2 and the aperture ratio of2.9-4.0 or thereabout. FIG. 21 shows an optical sectional view of thezoom lens according to the numerical example 6.

In the numerical example 6 shown in FIG. 21, the first lens unit ofnegative refractive power is composed of two lenses, i.e., in order fromthe object side to the image side, a negative lens 11 of meniscus formhaving a concave surface facing the image side, and a positive lens 12of meniscus form having a convex surface facing the object side.

The second lens unit of positive refractive power is composed of threelenses as a whole, i.e., in order from the object side to the imageside, a positive lens 21 of bi-convex form, a negative lens 22 ofbi-concave form, and a positive lens 23 of bi-convex form, and thenegative lens 22 and the positive lens 23 constitute a cemented lens.Further, the third lens unit of positive refractive power is composed ofa positive lens 31 having a convex surface facing the object side.

Further, during zooming from the wide-angle end to the telephoto end,the first lens unit makes a reciprocating motion convex toward the imageside, the second lens unit moves toward the object side, and the thirdlens unit moves with a locus convex toward the image side.

[Numerical Example 7]

The zoom lens according to the numerical example 7 is a zoom lens havingthe variable magnification ratio of about 2 and the aperture ratio of2.7-4.0 or thereabout. FIG. 25 shows an. optical sectional view of thezoom lens according to the numerical example 7.

In the numerical example 7 shown in FIG. 25, the first lens unit ofnegative refractive power is composed of two lenses, i.e., in order fromthe object side to the image side, a negative lens 11 of meniscus formhaving a concave surface facing the image side, and a positive lens 12of meniscus form having a convex surface facing the object side.

The second lens unit of positive refractive power is composed of threelenses as a whole, i.e., in order from the object side to the imageside, a positive lens 21 of bi-convex form, a negative lens 22 ofbi-concave form, and a positive lens 23 of bi-convex form, and thepositive lens 21 and the negative lens 22 constitute a cemented lens.Further, the third lens unit of positive refractive power is composed ofa positive lens 31 of bi-convex form.

Further, during zooming from the wide-angle end to the telephoto end,the first lens unit makes a reciprocating motion convex toward the imageside, the second lens unit moves toward the object side, and the thirdlens unit moves with a locus convex toward the image side.

[Numerical Example 8]

The zoom lens according to the numerical example 8 is a zoom lens havingthe variable magnification ratio of about 2 and the aperture ratio of2.8-4.0 or thereabout. FIG. 29 shows an optical sectional view of thezoom lens according to the numerical example 8.

In the numerical example 8 shown in FIG. 29, the first lens unit ofnegative refractive power is composed of two lenses, i.e., in order fromthe object side to the image side, a negative lens 11 of bi-concaveform, and a positive lens 12 of meniscus form having a convex surfacefacing the object side.

The second lens unit of positive refractive power is composed of threelenses as a whole, i.e., in order from the object side to the imageside, a positive lens 21 of bi-convex form, a positive lens 22 ofbi-convex form, and a negative lens 23 of bi-concave form, and thepositive lens 22 and the negative lens 23 constitute a cemented lens.Further, the third lens unit of positive refractive power is composed ofa positive lens 31 of bi-convex form.

Further, during zooming from the wide-angle end to the telephoto end,the first lens unit moves toward the object side, the second lens unitalso moves toward the object side, and the third lens unit moves with alocus convex toward the image side.

According to the second embodiment, with the respective lens elementsset as described above, in particular, the following advantageouseffects can be obtained in particular.

-   -   (d-1) It is possible to attain a zoom lens which is suited for a        photographic system using a solid-state image sensor, is compact        with less constituent lens elements, is corrected particularly        for chromatic aberration, and has excellent optical performance,        by disposing, in order from the object side to the image side, a        first lens unit of negative refractive power, a second lens unit        of positive refractive power and a third lens unit of positive        refractive power, effecting the variation of magnification by        varying the separations of the respective adjacent lens units,        constructing the first lens unit with two lenses, i.e., in order        from the object side to the image side, a concave lens and a        convex lens, constructing the second lens unit with three        lenses, i.e., in order from the object side to the image side, a        single convex lens and a cemented lens composed of a concave        lens and a convex lens, or a cemented lens composed of a convex        lens and a concave lens and a single convex lens, or a single        convex lens and a cemented lens composed of a convex lens and a        concave lens, and constructing the third lens unit with at least        one convex lens.    -   (d-2) It is possible to effectively correct the various        off-axial aberrations, such as astigmatism and distortion, and        spherical aberration due to the increase of an aperture ratio,        by effectively introducing an aspheric surface into each lens        unit.

Next, numerical data of the numerical examples 6 to 8 of the inventionare shown.

In addition, the values of the factors in the above-mentioned conditions(5) to (9) for the numerical examples 6 to 8 are listed in Table-2.

Numerical Example 6: f = 5.50-10.60 (mm) Fno = 2.9-4.0 2ω = 61.4°-34.4°R1 = 20.453 D1 = 1.20 N1 = 1.77250 ν1 = 49.6 R2 = 3.694* D2 = 0.90 R3 =5.082 D3 = 2.10 N2 = 1.80518 ν2 = 25.4 R4 = 8.267 D4 = Variable R5 =Stop D5 = 0.50 R6 = 13.292* D6 = 1.60 N3 = 1.73077 ν3 = 40.5 R7 =−12.248 D7 = 0.95 R8 = −4.673 D8 = 0.60 N4 = 1.76182 ν4 = 26.5 R9 =23.052 D9 = 2.00 N5 = 1.77250 ν5 = 49.6 R10 = −5.042* D10 = Variable R11= 19.454* D11 = 1.60 N6 = 1.60311 ν6 = 60.6 R12 = −1267.560 D12 =Variable R13 = ∞ D13 = 2.80 N7 = 1.51633 ν7 = 64.2 R14 = ∞ VariableFocal Length Separation 5.50 7.79 10.60 6.53 9.17 D4 7.52 4.27 1.72 5.892.88 D10 4.91 9.63 13.06 7.43 11.50 D12 3.41 1.68 1.23 2.38 1.30Aspheric Coefficients: R2 R = 3.69429e+00 K = −9.73942e−01 B =1.43792e−03 C = 2.73074e−05 D = 1.56359e−06 R6 R = 1.32924e+01 K =1.27994e+01 B = −7.85390e−04 C = −6.33445e−05 D = −9.01039e−07 R10 R =−5.04162e+00 K = 8.47026e−01 B = 1.28637e−03 C = 2.36015e−05 D =7.54790e−06 R11 R = 1.94539e+01 K = 0.00000e+00 B = −4.37109e−04 C =1.62332e−05 D = −1.26788e−06*Aspheric Surface

Numerical Example 7: f = 5.20-10.35 (mm) Fno = 2.8-4.0 2ω = 64.4°-35.2°R1 = 110.720 D1 = 1.20 N1 = 1.77250 ν1 = 49.6 R2 = 3.410* D2 = 1.02 R3 =5.803 D3 = 2.00 N2 = 1.80518 ν2 = 25.4 R4 = 18.549 D4 = Variable R5 =Stop D5 = 0.50 R6 = 4.856* D6 = 1.90 N3 = 1.77250 ν3 = 49.6 R7 = −9.078D7 = 0.50 N4 = 1.71736 ν4 = 29.5 R8 = 5.069 D8 = 0.42 R9 = 19.306 D9 =1.60 N5 = 1.69680 ν5 = 55.5 R10 = −14.532* D10 = Variable R11 = 508.660*D11 = 1.50 N6 = 1.69680 ν6 = 55.5 R12 = −13.714 D12 = Variable R13 = ∞D13 = 2.70 N7 = 1.51633 ν7 = 64.2 R14 = ∞ Variable Focal LengthSeparation 5.20 7.70 10.35 6.36 9.06 D4 7.89 4.60 2.13 6.21 3.26 D104.85 9.05 11.63 7.15 10.55 D12 2.21 1.20 1.81 1.50 1.30 AsphericCoefficients: R2 R = 3.41414e+00 K = −9.99930e−01 B = 1.00175e−03 C =1.62461e−05 D = −3.70217e−07 R6 R = 4.85608e+00 K = 7.96803e−01 B =−1.38408e−03 C = −4.51331e−05 D = −6.60254e−06 R10 R = −1.45325e+01 K =7.69796e+00 B = 1.06613e−03 C = 7.42392e−05 D = 2.58556e−06 R11 R =5.08660e+02 K = 0.00000e+00 B = −4.51399e−04 C = 2.67697e−06 D =−3.21647e−07*Aspheric Surface

Numerical Example 8: f = 6.24-11.97 (mm) Fno = 2.7-4.0 2ω = 55.4°-30.6°R1 = −408.296 D1 = 1.30 N1 = 1.77250 ν1 = 49.6 R2 = 5.731* D2 = 1.11 R3= 6.705 D3 = 2.00 N2 = 1.84666 ν2 = 23.8 R4 = 9.956 D4 = Variable R5 =Stop D5 = 0.70 R6 = 37.724* D6 = 1.60 N3 = 1.69680 ν3 = 55.5 R7 =−11.263 D7 = 0.15 R8 = 4.068* D8 = 1.90 N4 = 1.69680 ν4 = 55.5 R9 =−10.353 D9 = 0.50 N5 = 1.64769 ν5 = 33.8 R10 = 3.020 D10 = Variable R11= 130.261* D11 = 1.80 N6 = 1.60311 ν6 = 60.6 R12 = −8.133 D12 = VariableR13 = ∞ D13 = 2.70 N7 = 1.51633 ν7 = 64.2 R14 = ∞ Variable Focal LengthSeparation 6.24 8.99 11.97 7.54 10.50 D4 6.61 4.09 2.25 5.29 3.09 D104.30 8.27 11.64 6.37 10.03 D12 1.75 1.19 1.24 1.40 1.14 AsphericCoefficients: R2 R = 5.73088e+00 K = −1.98834e+00 B = 1.10448e−03 C =6.36136e−06 D = −1.55169e−07 R6 R = 3.77245e+01 K = −1.10342e+02 B =−1.46479e−04 C = 2.09594e−05 D = −3.06969e−06 R8 R = 4.06784e+00 K =−3.30676e−01 B = 4.58158e−04 C = 3.25580e−06 D = 2.67999e−06 R11 R =1.30261e+02 K = 0.00000e+00 B = −9.13704e−04 C = 2.07821e−05 D =−7.46835e−07*Aspheric Surface

TABLE 2 Numerical Example Condition 6 7 8 (5) nd 1.76182 1.71736 1.64769(6) νd 26.5 29.5 33.8 (7) X1 0.44 0.74 2.46 X3 2.29 1.03 0.61 |X1/X3|0.20 0.72 4.00 (8) DL1 4.20 4.22 4.41 DL2 5.15 4.42 4.15 DL3 1.60 1.501.80 DL 31.08 29.29 28.60 (DL1 + DL1 + DL3)/DL 0.35 0.35 0.36 (9) DA20.95 0.42 0.15 DD2 5.15 4.42 4.15 DA2/DD2 0.18 0.09 0.04

According to the second embodiment, It is possible to attain a zoom lenswhich is suited, in particular, for a photographic system using asolid-state image sensor, is compact with less constituent lenselements, and has excellent optical performance.

(Third Embodiment)

FIG. 33 to FIGS. 44A to 44D relate to a third embodiment of theinvention, which corresponds to numerical examples 9 to 11 of theinvention to be described later.

FIG. 33 is a lens block diagram showing a zoom lens according to thenumerical example 9 of the invention. FIGS. 34A to 34D through FIGS. 36Ato 36D are graphs showing aberration curves at the wide-angle end, themiddle focal length position and the telephoto end, respectively, in thezoom lens according to the numerical example 9 of the invention.

FIG. 37 is a lens block diagram showing a zoom lens according to thenumerical example 10 of the invention. FIGS. 38A to 38D through FIGS.40A to 40D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 10 of the invention.

FIG. 41 is a lens block diagram showing a zoom lens according to thenumerical example 11 of the invention. FIGS. 42A to 42D through FIGS.43A to 43D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 11 of the invention.

In the lens block diagrams shown in FIGS. 33, 37 and 41, referencecharacter L1 denotes a first lens unit of negative refractive power,reference character L2 denotes a second lens unit of positive refractivepower, reference character L3 denotes a third lens unit of positiverefractive power, reference character SP denotes an aperture stop,reference character IP denotes an image plane, and reference character Gdenotes a glass block, such as a filter or a color separation prism.

The zoom lens according to the third embodiment has three lens units,i.e., in order from the object side to the image side, the first lensunit L1 of negative refractive power, the second lens unit L2 ofpositive refractive power and the third lens unit L3 of positiverefractive power. During zooming from the wide-angle end to thetelephoto end, the first lens unit, the second lens unit and the thirdlens unit each move. More specifically, the first lens unit makes areciprocating motion convex toward the image side, the second lens unitmoves toward the object side, and the third lens unit moves toward theimage side or moves with a locus convex toward the object side.

In the zoom lens according to the third embodiment, the variation ofmagnification is effected mainly by moving the second lens unit whilethe shift of an image point due to the variation of magnification iscompensated for by moving forward and backward the first lens unit andmoving the third lens unit toward the image side or moving the thirdlens unit with a locus convex toward the object side.

The third lens unit shares the increase of a refractive power of thephotographic lens due to the reduction in size of the image sensor,thereby reducing a refractive power of the short zoom system composed ofthe first and second lens units, so that the occurrence of aberration bylenses constituting the first lens unit can be suppressed, so as toattain high optical performance. Further, the telecentric imageformation on the image side necessary for the photographing apparatus(optical apparatus) using the image sensor or the like is attained bygiving the third lens unit the roll of a field lens.

Further, the stop SP is disposed on the most object side of the secondlens unit, thereby shortening the distance between the entrance pupiland the first lens unit on the wide-angle side, so that the increase ofthe diameter of lenses constituting the first lens unit can beprevented. In addition, the various off-axial aberrations are canceledby the first lens unit and the third lens unit across the stop disposedon the object side of the second lens unit, so that good opticalperformance can be obtained without increasing the number of constituentlenses.

The zoom lens according to the third embodiment is characterized in thatthe third lens unit has at least one positive lens, and the followingconditions are satisfied:ndp3<1.5  (10)vdp3<70.0  (11)where ndp3 and vdp3 are a refractive index and Abbe number,respectively, of material of the positive lens of the third lens unit.

The conditions (10) and (11) are provided mainly for correcting wellcurvature of field and lateral chromatic aberration. If the upper limitof the condition (10) is exceeded, the Petzval Sum increases in thenegative direction, so that it becomes difficult to correct curvature offield. Further, if the upper limit of the condition (11) is exceeded, itbecomes disadvantageously difficult to correct lateral chromaticaberration at the telephoto end.

In addition, with the zoom lens according to the third embodimentconstructed as described in the foregoing, the primary object of theinvention can be attained. However, in order to obtain better opticalperformance or in order to attain the reduction in size of the entirelens system, it is preferable to satisfy at least one of the followingconditions (e-1) to (e-16).

-   -   (e-1) During the variation of magnification from the wide-angle        end to the telephoto end, the first lens unit moves with a locus        convex toward the image side, the second lens unit moves        monotonically toward the object side, and the third lens unit        moves toward the image side.    -   (e-2) The first lens unit consists of two lenses, i.e., a        negative lens and a positive lens, and at least one surface of        the negative lens of the first lens unit is an aspheric surface.

In the zoom lens according to the third embodiment, the first lens unitof negative refractive power has the role of causing an off-axialprincipal ray to be pupil-imaged on the center of a stop, and,particularly, on the wide-angle side, the amount of refraction of anoff-axial principal ray is large. Therefore, in the first lens unit, thevarious off-axial aberrations, particularly, astigmatism and distortion,are apt to occur.

Accordingly, similarly to an ordinary wide-angle lens, the first lensunit is made to have the construction having a negative lens and apositive lens so as to prevent the diameter of a lens disposed on themost object side from increasing. Further, it is more preferable that alens surface on the image side of the negative lens 11 of meniscus formis such an aspheric surface that a negative refractive power becomesprogressively weaker toward a marginal portion of the lens surface. Bythis arrangement, astigmatism and distortion are corrected in awell-balanced manner, and the first lens unit is composed of such asmall number of lenses as two, so that it becomes easy to make theentire lens system compact.

In addition, in order to prevent the occurrence of an off-axialaberration due to the refraction of an off-axial principal ray, each oflenses constituting the first lens unit has a lens surface approximateto concentric spherical surfaces having the center on a point at whichthe stop and the optical axis intersect.

-   -   (e-3) The following conditions are satisfied:        ndn1>1.70  (12)        vdn1>35.0  (13)        where ndn1 and vdn1 are a refractive index and Abbe number,        respectively, of material of a negative lens included in the        first lens unit.

The conditions (12) and (13) are provided for making the compactness ofthe entire lens system and the good imaging performance compatible witheach other.

If the upper limit of the condition (12) is exceeded, the Petzval sum ofthe first lens unit increases in the positive direction, so that itbecomes difficult to correct curvature of field.

Further, if the upper limit of the condition (13) is exceeded, itbecomes disadvantageously difficult to correct lateral chromaticaberration at the wide-angle end, in particular.

-   -   (e-4) The second lens unit consists of two cemented lenses.

In the third embodiment, in order to cope with the reduction of theamount of chromatic aberration, which is required according to theincreased number of pixels and the minimization of cell pitches of asolid-state image sensor such as a CCD, the second lens unit consists oftwo cemented lenses, i.e., a first cemented lens composed of a positivelens 21 of meniscus form and a negative lens 22 of meniscus formcemented together, and a second cemented lens composed of a negativelens 23 and a positive lens 24 cemented together. By this arrangement,it is possible to correct well longitudinal chromatic aberration andlateral chromatic aberration.

Further, with the second lens unit consisting of two cemented lenses,the following advantages are obtained. Since a refractive power of theconcave (negative) lens component in the so-called triplet type isseparated into two components, the degree of freedom of the correctionof aberration is increased as against an aberration correcting methodusing such a single concave lens component as that in the triplet type.Accordingly, it becomes unnecessary to correct off-axial flare, which,otherwise, is corrected by increasing the glass thickness of the concavelens component, or to correct spherical aberration due to two negativeair lenses provided before and behind the concave lens component.Therefore, it becomes possible to lessen the thickness on the opticalaxis of the second lens unit as compared with the triplet type. Thus,the second lens unit composed of two cemented lenses contributes to theshortening of the entire optical system and the shortening of the totallength of the lens system as retracted.

-   -   (e-5) The second lens unit has, on the most object side thereof,        a first cemented lens composed of a positive lens having a        convex surface facing the object side and a negative lens having        a concave surface facing the image side, a lens surface on the        object side of the positive lens of the first cemented lens is        an aspheric surface, and the following condition is satisfied:        0<(R 21−R 23)/(R 21+R 23)<0.1  (14)        where R21 is a radius of paraxial curvature of the lens surface        on the object side of the positive lens of the first cemented        lens, and R23 is a radius of paraxial curvature of a lens        surface on the image side of the negative lens of the first        cemented lens.

If the upper limit of the condition (14) is exceeded, the Petzval sum ofthe second lens unit increases in the negative direction, so that itbecomes difficult to correct curvature of field.

If the lower limit of the condition (14) is exceeded, it becomesdisadvantageously difficult to correct spherical aberration and coma.

-   -   (e-6) The second lens unit has a positive lens disposed on the        most image side thereof, and the following conditions are        satisfied:        ndp2>1.70  (15)        vdp2>40.0  (16)        where ndp2 and vdp2 are a refractive index and Abbe number,        respectively, of material of the positive lens of the second        lens unit.

If the upper limit of the condition (15) is exceeded, the Petzval sumincreases in the negative direction, so that it becomes difficult tocorrect curvature of field. Further, if the upper limit of the condition(16) is exceeded, it becomes disadvantageously difficult to correctlongitudinal chromatic aberration at the telephoto end.

-   -   (e-7) The third lens unit consists of one positive lens.

The third lens unit of positive refractive power consists of onepositive lens 31 having a convex surface facing the object side, andserves also as a field lens for making the zoom lens telecentric on theimage side.

-   -   (e-8) One positive lens of the third lens unit has at least one        aspheric surface.

In particular, in the third embodiment, it is preferable that a lenssurface on the image side of the convex lens 31 is such an asphericsurface that a positive refractive power becomes progressively weakertoward a marginal portion of the lens surface. By this arrangement, itis possible to correct the various off-axial aberrations over the entirezooming range.

-   -   (e-9) Focusing from an infinitely distant object to a closest        object is effected by moving the third lens unit toward the        object side.

When focusing from an infinitely distant object to a closest object iseffected by using the zoom lens according to the third embodiment, thegood optical performance can be obtained by moving the first lens unittoward the object side. However, it is more preferable to move the thirdlens unit toward the object side.

This arrangement prevents the increase of the diameter of a front lensmember due to the focusing movement of the first lens unit which isdisposed on the most object side, prevents the increase of the load onan actuator for moving the first lens unit which is the heaviest amongthe lens units, and makes it possible to move, during zooming, the firstlens unit and the second lens unit in an interlocking relation simplywith a cam or the like used. Therefore, it is possible to attain thesimplification of a mechanism and the enhancement of precision thereof.

Further, in a case where focusing is performed by using the third lensunit, if the third lens unit is arranged to be moved toward the imageside during the variation of magnification from the wide-angle end tothe telephoto end, the telephoto end, at which the amount of movementfor focusing is large, can be located on the image side. Accordingly, itbecomes possible to minimize the amount of total movement of the thirdlens unit required for zooming and focusing. This arrangement makes itpossible to attain the compactness of the entire lens system.

-   -   (e-10) The following condition is satisfied:        0.25<(L 1+L 2+L 3)/L<0.45  (17)        where L is a distance, at the telephoto end, from a vertex on        the object side of a lens disposed on the most object side of        the first lens unit to an image plane, L1 is a distance from the        vertex on the object side of the lens disposed on the most        object side of the first lens unit to a vertex on the image side        of a lens disposed on the most image side of the first lens        unit, L2 is a distance from a vertex on the object side of a        lens disposed on the most object side of the second lens unit to        a vertex on the image side of a lens disposed on the most image        side of the second lens unit, and L3 is a distance from a vertex        on the object side of a lens disposed on the most object side of        the third lens unit to a vertex on the image side of a lens        disposed on the most image side of the third lens unit.

If the upper limit of the condition (17) is exceeded, although the totallength of the optical system at the telephoto end becomes short, the sumof lengths of the respective lens units on the optical axis becomeslarge, so that the total length of the entire lens system as retractedbecomes long disadvantageously.

If the lower limit of the condition (17) is exceeded, although the sumof lengths of the respective lens units on the optical axis becomessmall, the total length of the optical system at the telephoto endbecomes long, and the amount of movement of each lens unit isnecessarily increased. Therefore, the length of a cam ring or the likefor moving each lens unit becomes long, and, as a result, the totallength of the entire lens system as retracted does not become short.

-   -   (e-11) The following condition is satisfied:        0.05<A 2/D 2<0.2  (18)        where D2 is the sum of thicknesses on the optical axis of lenses        constituting the second lens unit, and A2 is the sum of air        separations included in the second lens unit.

If the upper limit of the condition (18) is exceeded, the length of thesecond lens unit on the optical axis becomes long, so that it becomesdisadvantageously difficult to attain the compactness of the opticalsystem.

If the lower limit of the condition (18) is exceeded, the power of theair lens becomes small, so that it becomes disadvantageously difficultto correct spherical aberration.

-   -   (e-12) The first lens unit of negative refractive power consists        of two lenses, i.e., in order from the object side to the image        side, a negative lens 11 of meniscus form having a concave        surface facing the image side, and a positive lens 12 of        meniscus form having a convex surface facing the object side, or        consists of three lenses, i.e., in order from the object side to        the image side, a negative lens 11 of meniscus form having a        convex surface facing the object side, a negative lens 12 of        meniscus form having a convex surface facing the object side,        and a positive lens 13 of meniscus form having a convex surface        facing the object side, the second lens unit of positive        refractive power consists of four lenses, i.e., in order from        the object side to the image side, a positive lens 21 of        meniscus form having a concave surface facing the image side, a        negative lens 22 of meniscus form having a convex surface facing        the object side, a negative lens 23 of meniscus form having a        convex surface facing the object side, and a positive lens 24 of        bi-convex form, the positive lens 21 and the negative lens 22        constituting a cemented lens, the negative lens 23 and the        positive lens 24 constituting a cemented lens, and the third        lens unit of positive refractive power consists of a positive        lens 31 having a convex surface facing the image side or a        cemented lens composed of a negative lens and a positive lens.

By this arrangement, it is possible to easily attain the compactness ofa lens system while keeping good optical performance.

-   -   (e-13) The second lens unit of positive refractive power has, on        the most object side thereof, a positive lens 21 having a strong        convex surface facing the object side. By this arrangement, it        is possible to lessen the angle of refraction of an off-axial        principal ray having exited from the first lens unit, thereby        preventing the various off-axial aberrations from occurring.    -   (e-14) A positive lens 21 included in the second lens unit is a        lens arranged to allow an on-axial ray to pass at the largest        height, and is concerned with the correction of, mainly,        spherical aberration and coma. Therefore, it is preferable that        a lens surface on the object side of the positive lens 21 is        such an aspheric surface that a positive refractive power        becomes progressively weaker toward a marginal portion of the        lens surface. By this arrangement, it becomes easy to correct        well spherical aberration and coma.    -   (e-15) A negative lens 22 disposed on the image side of a        positive lens 21 on the object side included in the second lens        unit is made to have a concave surface facing the image side, so        that a negative air lens is formed by the concave surface on the        image side of the negative lens 22 and a convex surface on the        object side of a negative lens 23 disposed subsequent to the        negative lens 22. By this arrangement, it is possible to correct        spherical aberration occurring due to the increase of an        aperture ratio.    -   (e-16) When the back focal distance is denoted by sk′, the focal        length of the third lens unit is denoted by f3, and the image        magnification of the third lens unit is denoted by β3, the        following relation is obtained:        sk′=f 3(1−β3)        provided that 0<β3<1.0.

Here, when the third lens unit is moved toward the image side during thevariation of magnification from the wide-angle end to the telephoto end,the back focal distance sk′ decreases, so that the image magnificationβ3 of the third lens unit increases on the telephoto side. Then, as aresult, the third lens unit shares the variation of magnification withthe second lens unit, so that the amount of movement of the second lensunit is reduced. Therefore, since such a space for the movement of thesecond lens unit can be saved, the third lens unit contributes to thereduction in size of the lens system.

Next, characteristic features of the lens construction of each of thezoom lenses according to the numerical examples 9 to 11 are described.

[Numerical Example 9]

The zoom lens according to the numerical example 9 shown in FIG. 33 is azoom lens having the variable magnification ratio of about 3 and theaperture ratio of 2.7-4.8 or thereabout.

[Numerical Example 10]

In the zoom lens according to the numerical example 10 shown in FIG. 37,during zooming from the wide-angle end to the telephoto end, the firstlens unit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side.

In the numerical example 10, the first lens unit consists of threelenses, i.e., in order from the object side to the image side, anegative lens 11 of meniscus form, a negative lens 12 of meniscus formand a positive lens 13 of meniscus form, so that it is possible toeasily attain the further widening of an angle of view as compared witha zoom lens in which the first lens unit is composed of two lenses.

The zoom lens according to the numerical example 10 is a zoom lenshaving the variable magnification ratio of about 3 and the apertureratio of 2.6-4.8 or thereabout.

[Numerical Example 11]

In the zoom lens according to the numerical example 11 shown in FIG. 41,during zooming from the wide-angle end to the telephoto end, the firstlens unit makes a reciprocating motion convex toward the image side, thesecond lens unit moves toward the object side, and the third lens unitmoves toward the image side.

In the numerical example 11, the third lens unit consists of a cementedlens composed of a negative lens of meniscus form and a positive lens ofbi-convex form, thereby sufficiently correcting chromatic aberration inconjunction with two cemented lenses of the second lens unit.

The zoom lens according to the numerical example 11 is a zoom lenshaving the variable magnification ratio of about 3.0 and the apertureratio of 2.7-4.8 or thereabout.

Next, numerical data of the numerical examples 9 to 11 of the inventionare shown.

In addition, the values of the factors in the above-mentioned conditions(10) to (18) for the numerical examples 9 to 11 are listed in Table-3.

Numerical Example 9: R1 = 206.343 D1 = 1.40 N1 = 1.80238 ν1 = 40.7 R2 =4.841* D2 = 1.87 R3 = 9.750 D3 = 2.00 N2 = 1.84666 ν2 = 23.9 R4 = 49.125D4 = Variable R5 = Stop D5 = 0.70 R6 = 4.564* D6 = 2.00 N3 = 1.74330 ν3= 49.3 R7 = 10.675 D7 = 0.80 N4 = 1.69895 ν4 = 30.1 R8 = 3.878 D8 = 0.72R9 = 10.459 D9 = 0.50 N5 = 1.84666 ν5 = 23.9 R10 = 6.339 D10 = 1.80 N6 =1.60311 ν6 = 60.6 R11 = −19.132 D11 = Variable R12 = 14.948 D12 = 1.40N7 = 1.48749 ν7 = 70.2 R13 = −48.563 D13 = Variable R14 = ∞ D14 = 2.82N8 = 1.51633 ν8 = 64.1 R15 = ∞ Variable Focal Length Separation 5.4910.60 16.18 D4 16.12 5.84 2.43 D11 3.93 11.43 19.83 D13 4.20 3.82 2.53Aspheric Coefficients: R2 R = 4.84094e+00 K = −1.84876e+00 B =1.10500e−03 C = −1.66493e−05 D = 5.13200e−07 E = −2.00144e−08 F =3.39222e−10 R6 R = 4.56367e+00 K = −1.26047e−01 B = −2.89482e−04 C =−9.34418e−06 D = 1.07843e−07 E = −3.76119e−08*Aspheric Surface

Numerical Example 10: R1 = 59.735 D1 = 1.30 N1 = 1.67470 ν1 = 54.9 R2 =6.518* D2 = 2.02 R3 = 21.785 D3 = 0.80 N2 = 1.77250 ν2 = 49.6 R4 = 8.687D4 = 1.48 R5 = 11.006 D5 = 2.00 N3 = 1.84666 ν3 = 23.9 R6 = 33.156 D6 =Variable R7 = Stop D7 = 0.80 R8 = 4.526* D8 = 2.20 N4 = 1.74330 ν4 =49.3 R9 = 11.087 D9 = 0.60 N5 = 1.69895 ν5 = 30.1 R10 = 3.873 D10 = 0.75R11 = 10.369 D11 = 0.50 N6 = 1.84666 ν6 = 23.9 R12 = 6.401 D12 = 1.80 N7= 1.60311 ν7 = 60.6 R13 = −19.975 D13 = Variable R14 = 12.110* D14 =1.50 N8 = 1.48749 ν8 = 70.2 R15 = −54.317 D15 = Variable R16 = ∞ D16 =2.83 N9 = 1.51633 ν9 = 64.1 R17 = ∞ Variable Focal Length Separation5.00 9.79 14.98 D6 14.64 5.46 2.12 D13 4.83 13.24 21.64 D15 3.55 3.022.51 Aspheric Coefficients: R2 R = 6.51783e+00 K = 2.42523e−01 B =−5.97797e−04 C = −1.56333e−06 D = −7.09941e−07 E = 2.27735e−08 F =−6.39051e−10 R8 R = 4.52644e+00 K = −1.27422e−01 B = −3.12555e−04 C =−9.46539e−06 D = 8.23854e−08 E = −3.89693e−08 R14 R = 1.21103e+01 K = 0B = −1.72597e−04 C = 7.00489e−06 D = −1.67824e−07*Aspheric Surface

Numerical Example 11: R1 = 156.481 D1 = 1.30 N1 = 1.80238 ν1 = 40.7 R2 =5.435* D2 = 1.83 R3 = 9.697 D3 = 2.20 N2 = 1.84666 ν2 = 23.9 R4 = 34.098D4 = Variable R5 = Stop D5 = 0.80 R6 = 4.588* D6 = 2.00 N3 = 1.74330 ν3= 49.3 R7 = 13.399 D7 = 0.60 N4 = 1.69895 ν4 = 30.1 R8 = 3.929 D8 = 0.66R9 = 11.757 D9 = 0.60 N5 = 1.84666 ν5 = 23.9 R10 = 7.899 D10 = 1.70 N6 =1.60311 ν6 = 60.6 R11 = −20.079 D11 = Variable R12 = 25.476 D12 = 0.50N7 = 1.60342 ν7 = 38.0 R13 = 24.901 D13 = 1.60 N8 = 1.49700 ν8 = 81.5R14 = −25.962 D14 = Variable R15 = ∞ D15 = 2.80 N9 = 1.51633 ν9 = 64.1R16 = ∞ Variable Focal Length Separation 5.64 10.99 16.51 D4 18.32 6.102.69 D11 3.11 9.75 18.27 D14 4.42 4.42 2.54 Aspheric Coefficients: R2 R= 5.43534e+00 K = −2.28361e+00 B = 1.23160e−03 C = −2.40093e−05 D =8.92996e−07 E = −2.78071e−08 F = 3.81774e−10 R6 R = 4.58844e+00 K =−1.27107e−01 B = −2.62331e−04 C = −8.61678e−06 D = 1.99209e−07 E =−3.78975e−08*Aspheric Surface

TABLE 3 Condition lower upper Numerical Example limit limit 9 10 11 (10)ndp3 1.5 1.48749 1.48749 1.49700 (11) νdp3 70 70.2 70.2 81.5 (12) ndn11.7 1.80238 — 1.80238 (13) νdn1 35 40.7 — 40.7 (14) R21 4.564 4.5264.588 R23 3.878 3.873 3.929 (R21 − R23)/ 0 0.1 0.081 0.078 0.077 (R21 +R23) (15) ndp2 1.7 1.74330 1.74330 1.74330 (16) νdp2 40 49.3 49.3 49.3(17) L1 5.27 7.60 5.33 L2 5.82 5.85 5.56 L3 1.40 1.50 2.10 L 41.74 45.7841.28 (L1 + L2 + 0.25 0.45 0.30 0.33 0.31 L3)/L (18) A2 0.72 0.75 0.66D2 5.82 5.85 5.56 A2/D2 0.05 0.2 0.12 0.13 0.12

According to the third embodiment of the invention, it is possible toattain a zoom lens which is suited for a photographic system using asolid-state image sensor, has a high variable magnification ratiodespite being compact and small in diameter with less constituent lenselements, and has excellent optical performance.

(Fourth Embodiment)

FIG. 45 to FIGS. 60A to 60D relate to a fourth embodiment of theinvention, which corresponds to numerical examples 12 to 15 of theinvention to be described later.

FIG. 45 is a lens block diagram showing a zoom lens according to thenumerical example 12 of the invention. FIGS. 46A to 46D through FIGS.48A to 48D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 12 of the invention.

FIG. 49 is a lens block diagram showing a zoom lens according to thenumerical example 13 of the invention. FIGS. 50A to 50D through FIGS.52A to 52D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 13 of the invention.

FIG. 53 is a lens block diagram showing a zoom lens according to thenumerical example 14 of the invention. FIGS. 54A to 54D through FIGS.56A to 56D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 14 of the invention.

FIG. 57 is a lens block diagram showing a zoom lens according to thenumerical example 15 of the invention. FIGS. 58A to 58D through FIGS.60A to 60D are graphs showing aberration curves at the wide-angle end,the middle focal length position and the telephoto end, respectively, inthe zoom lens according to the numerical example 15 of the invention.

In the lens block diagrams shown in FIGS. 45, 49, 53 and 57, referencecharacter L1 denotes a first lens unit of negative refractive power,reference character L2 denotes a second lens unit of positive refractivepower, reference character L3 denotes a third lens unit of positiverefractive power, reference character SP denotes an aperture stop fordetermining the brightness of an optical system, reference character IPdenotes an image plane, and reference character G denotes a glass block,such as a filter or a color separation prism.

As shown in the lens block diagrams of FIGS. 45, 49, 53 and 57, the zoomlens according to the fourth embodiment has three lens units, i.e., inorder from the object side to the image side, the first lens unit L1 ofnegative refractive power, the second lens unit L2 of positiverefractive power and the third lens unit L3 of positive refractivepower. During the variation of magnification from the wide-angle end tothe telephoto end, as indicated by the arrows shown in the lens blockdiagrams shown in FIGS. 45, 49, 53 and 57, the first lens unit L1 makesa reciprocating motion convex toward the image side, the second lensunit moves toward the object side, and the third lens unit moves towardthe image side.

The zoom lens according to the fourth embodiment has the basicconstruction as described above. Then, according to the fourthembodiment, it is possible to attain a zoom lens having high opticalperformance, by making the zoom lens have such a lens construction as tosatisfy at least one of the following conditions (19) to (22):0.08<M 3/fw<0.4  (19)0.7<|f 1/ft|<1.0  (20)1.45<f 3/ft<2.0  (21)0.63<f 2/ft<0.8  (22)where M3 is an amount of movement of the third lens unit toward theimage side during the variation of magnification from the wide-angle endto the telephoto end with an infinitely distant object focused on, fwand ft are focal lengths of the zoom lens at the wide-angle end and thetelephoto end, respectively, and f1, f2 and f3 are focal lengths of thefirst lens unit, the second lens unit and the third lens unit,respectively.

Next, characteristic features of the lens construction of the zoom lensaccording to the fourth embodiment are described.

The first lens unit when the zoom lens is at the telephoto end islocated at about the same position as when the zoom lens is at thewide-angle end, or is located slightly nearer to the image side thanwhen the zoom lens is at the wide-angle end. Accordingly, the amount ofmovement of the first lens unit required when the zoom lens is retractedis prevented from becoming too large.

The aperture stop SP is disposed on the object side of the second lensunit L2, and is arranged to move along the optical axis integrally withthe second lens unit.

In the zoom lens according to the fourth embodiment, the variation ofmagnification is effected mainly by moving the second lens unit ofpositive refractive power while the shift of an image point due to thevariation of magnification is compensated for by moving forward andbackward the first lens unit of negative refractive power and moving thethird lens unit of positive refractive power toward the image side.

The third lens unit of positive refractive power shares the increase ofa refractive power of the photographic lens due to the reduction in sizeof the image sensor, thereby reducing a refractive power of the shortzoom system composed of the first and second lens units, so that theoccurrence of aberration by lenses constituting the first lens unit canbe suppressed, so as to attain high optical performance. Further, inparticular, the telecentric image formation on the image side necessaryfor the optical apparatus using the image sensor or the like is attainedby giving the third lens unit the roll of a field lens.

Further, the stop SP is disposed on the most object side of the secondlens unit, thereby shortening the distance between the entrance pupiland the first lens unit on the wide-angle side, so that the increase ofthe diameter of lenses constituting the first lens unit can beprevented. In addition, the various off-axial aberrations are canceledby the first lens unit and the third lens unit across the stop disposedon the object side of the second lens unit, so that good opticalperformance can be obtained without increasing the number of constituentlenses.

Further, in the fourth embodiment, the first lens unit of negativerefractive power is composed of two lenses, i.e., in order from theobject side to the image side, a negative lens 11 having a concavesurface facing the image side, and a positive lens 12 of meniscus formhaving a convex surface facing the object side, the second lens unit ofpositive refractive power is composed of four lenses, i.e., a positivelens 21 of bi-convex form, a negative lens 22 of bi-concave form, anegative lens 23 of meniscus form having a convex surface facing theobject side, and a positive lens 24 of bi-convex form, the positive lens21 and the negative lens 22 constituting a cemented lens, the negativelens 23 and the positive lens 24 constituting a cemented lens, and thethird lens unit of positive refractive power is composed of a singlepositive lens 31 having a strong convex surface facing the object side.

With the respective lens units having such a lens construction as tomake the desired refractive power arrangement and the correction ofaberration compatible with each other, as described above, it ispossible to attain the compactness of a lens system while keeping thegood optical performance of the lens system. The first lens unit ofnegative refractive power has the role of causing an off-axial principalray to be pupil-imaged on the center of a stop, and, particularly, onthe wide-angle side, the amount of refraction of an off-axial principalray is large. Therefore, in the first lens unit, the various off-axialaberrations, particularly, astigmatism and distortion, are apt to occur.Accordingly, similarly to an ordinary wide-angle lens, the first lensunit is made to have the construction having a negative lens and apositive lens so as to prevent the diameter of a lens disposed on themost object side from increasing. Further, it is preferable that a lenssurface on the image side of the negative lens 11 is such an asphericsurface that a negative refractive power becomes progressively weakertoward a marginal portion of the lens surface. By this arrangement,astigmatism and distortion are corrected in a well-balanced manner, andthe first lens unit is composed of such a small number of lenses as two,so that it becomes easy to make the entire lens system compact.

The second lens unit of positive refractive power has, on the mostobject side thereof, the positive lens 21 having a strong convex surfacefacing the object side, so that the second lens unit has such a shape asto lessen the angle of refraction of an off-axial principal ray havingexited from the first lens unit, thereby preventing the variousoff-axial aberrations from occurring. Further, the positive lens 21 is alens arranged to allow an on-axial ray to pass at the largest height,and is concerned with the correction of, mainly, spherical aberrationand coma. In the fourth embodiment, it is preferable that a lens surfaceon the object side of the positive lens 21 is such an aspheric surfacethat a positive refractive power becomes progressively weaker toward amarginal portion of the lens surface. By this arrangement, it becomeseasy to correct well spherical aberration and coma. Further, thenegative lens 22 disposed on the image side of the positive lens 21 ismade to have a concave surface facing the image side, so that a negativeair lens is formed by the lens surface on the image side of the negativelens 22 and a convex surface on the object side of the negative lens 23disposed subsequent to the negative lens 22. Accordingly, it is possibleto correct spherical aberration occurring due to the increase of anaperture ratio.

In addition, in the fourth embodiment, in order to cope with thereduction of the amount of chromatic aberration, which is requiredaccording to the increased number of pixels and the minimization of cellpitches of a solid-state image sensor such as a CCD, the second lensunit is composed of two cemented lenses. By this arrangement, it ispossible to correct well longitudinal chromatic aberration and lateralchromatic aberration.

In the zoom lens according to the fourth embodiment, the third lens unitis moved toward the image side to make the third lens unit have thefunction of the variation of magnification and to lessen the burden ofthe variation of magnification imposed on the second lens unit, so thatthe amount of movement of the second lens unit is reduced, therebyattaining the reduction in the total lens length.

Next, the technical significance of each of the above-mentionedconditions (19) to (22) and the lens construction other than thatmentioned in the foregoing are described.

-   -   (f-1) The condition (19) is provided mainly for reducing the        size of the entire lens system.

If the amount of movement of the third lens unit becomes too smallbeyond the lower limit of the condition (19), the contribution of thethird lens unit concerning the variation of magnification becomes small,necessitating moving the second lens unit much to that extent, so thatthe reduction in size of the lens system becomes insufficient. On theother hand, if the upper limit of the condition (19) is exceeded, itbecomes difficult to secure the back focal distance at the telephotoend.

-   -   (f-2) The condition (20) is provided mainly for appropriately        setting the refractive power of the first lens unit so as to        correct well the various aberrations, such as distortion and        curvature of field, as well as to secure the sufficient back        focal distance, thereby attaining high optical performance.

If the focal length of the first lens unit becomes short beyond thelower limit of the condition (20), it becomes difficult to correct thevariation of distortion or curvature of field during the variation ofmagnification. On the other hand, if the upper limit of the condition(20) is exceeded, it becomes difficult to secure the back focaldistance.

-   -   (f-3) When a close-distance object is to be photographed by        using the zoom lens according to the fourth embodiment, the good        optical performance can be obtained by moving the first lens        unit toward the object side. However, it is preferable to move        the third lens unit also toward the object side. This        arrangement prevents the increase of the diameter of a front        lens member due to the focusing movement of the first lens unit        which is disposed on the most object side, prevents the increase        of the load on an actuator for moving the first lens unit which        is the heaviest among the lens units, and makes it possible to        move, during zooming, the first lens unit and the second lens        unit in an interlocking relation simply with a cam or the like        used. Therefore, it is possible to attain the simplification of        a mechanism and the enhancement of precision thereof.    -   (f-4) The condition (21) is provided for making the zoom lens        have a more telecentric construction than the two-unit        construction merely composed of a negative lens unit and a        positive lens unit, by additionally providing the third lens        unit of positive refractive power, and is provided for making        the effect of the telecentric construction sufficient.

If the focal length of the third lens unit becomes too short beyond thelower limit of the condition (21), the composite focal length of thefirst lens unit and the second lens unit becomes long to that extent, sothat the compactness of the entire lens system becomes insufficient. Onthe other hand, if the upper limit of the condition (21) is exceeded,the exit pupil becomes too short, in particular, at the wide-angle end,and, in a case where focusing is effected by using the third lens unit,the amount of movement required for focusing increasesdisadvantageously.

-   -   (f-5) The condition (22) is provided for reducing the amount of        movement of the second lens unit required for the variation of        magnification, to attain the reduction in size of the entire        lens system.

If the focal length of the second lens unit becomes short beyond thelower limit of the condition (22), although an advantage arises inreducing the size of the lens system, the Petzval sum becomes too largein the positive direction, so that it becomes difficult to correctcurvature of field. On the other hand, if the upper limit of thecondition (22) is exceeded, the amount of movement of the second lensunit required for the variation of magnification becomes large, so thatit becomes difficult to attain the reduction in size of the lens system.

-   -   (f-6) In the fourth embodiment, with the second lens unit        consisting of two cemented lenses, the following advantages are        obtained. Since a refractive power of the concave (negative)        lens component in the so-called triplet type is separated into        two components, the degree of freedom of the correction of        aberration is increased as against an aberration correcting        method using such a single concave lens component as that in the        triplet type. Accordingly, it becomes unnecessary to correct        off-axial flare, which, otherwise, is corrected by increasing        the glass thickness of the concave lens component, or to correct        spherical aberration due to two negative air lenses provided        before and behind the concave lens component. Therefore, it        becomes possible to lessen the thickness on the optical axis of        the second lens unit as compared with the triplet type. Thus,        the second lens unit composed of two cemented lenses contributes        to the shortening of the entire optical system and the        shortening of the total length of the lens system as retracted.    -   (f-7) It is desirable that the third lens unit is composed of a        single positive lens, from the viewpoints of the size of the        lens system and the reduction of load imposed on an actuator        required for focusing. In this instance, it is preferable to        satisfy the following condition:        −1.5<(R 3 f+R 3 r)/(R 3 f−R 3 r)<−0.5  (23)        where R3f is a radius of curvature of a lens surface on the        object side of the single positive lens, and R3r is a radius of        curvature of a lens surface on the image side of the single        positive lens.

The condition (23) is provided for, when the third lens unit is a singlepositive lens of spherical form, appropriately setting the shape of thesingle positive lens so as to enable focusing to be effected whilelessening the variation of aberration.

If the lower limit of the condition (23) is exceeded, the ghostoccurring due to the interreflection between the image pickup surfaceand the lens surface on the object side of the single positive lens ofthe third lens unit becomes apt to be formed in the vicinity of theimage pickup surface. If it is intended to avoid this ghost, it becomesnecessary to take the excessive back focal distance, thereby making itdifficult to sufficiently reduce the size of the lens system. On theother hand, if the upper limit of the condition (23) is exceeded, in acase where focusing is effected by using the third lens unit, it becomesdifficult to correct spherical aberration and astigmatism caused by thefocusing.

-   -   (f-8) If such an aspheric surface that a positive refractive        power becomes progressively weaker toward a marginal portion        thereof is introduced into the third lens unit, it is possible        to further reduce the variation of astigmatism during the        variation of magnification.

According to the fourth embodiment of the invention, it is possible toattain a zoom lens which is suited for a photographic system using asolid-state image sensor, is compact with less constituent lenselements, is corrected particularly for chromatic aberration, and hasexcellent optical performance, by constructing the zoom lens with threelens units, i.e., in order from the object side to the image side, afirst lens unit of negative refractive power, a second lens unit ofpositive refractive power and a third lens unit of positive refractivepower, effecting the variation of magnification by varying theseparation between the respective adjacent lens units, and appropriatelysetting the refractive power arrangement, the amount of movement and theshape of each lens unit.

Further, it is possible to effectively correct the various off-axialaberrations, particularly, astigmatism and distortion, and sphericalaberration caused by the increase of an aperture ratio, by introducingan aspheric surface into each lens unit.

Next, numerical data of the numerical examples 12 to 15 of the inventionare shown.

In addition, the values of the factors in the above-mentioned conditions(19) to (23) for the numerical examples 12 to 15 are listed in Table-4.

Numerical Example 12: f = 1-2.83 Fno = 2.87-4.90 2ω = 59.5°-22.8° R1 =10.855 D1 = 0.21 N1 = 1.802380 ν1 = 40.8 R2 = 0.830* D2 = 0.31 R3 =1.545 D3 = 0.29 N2 = 1.846660 ν2 = 23.9 R4 = 4.768 D4 = Variable R5 =Stop D5 = 0.11 R6 = 0.885* D6 = 0.43 N3 = 1.802380 ν3 = 40.8 R7 = −5.079D7 = 0.10 N4 = 1.698947 ν4 = 30.1 R8 = 0.720 D8 = 0.08 R9 = 2.210 D9 =0.09 N5 = 1.698947 ν5 = 30.1 R10 = 0.944 D10 = 0.31 N6 = 1.603112 ν6 =60.6 R11 = −3.065 D11 = Variable R12 = 2.292 D12 = 0.21 N7 = 1.518229 ν7= 58.9 R13 = 144.538 D13 = 0.43 R14 = ∞ D14 = 0.44 N8 = 1.516330 ν8 =64.1 R15 = ∞ Variable Focal Length Separation 1.00 2.41 2.83 D4 2.570.54 0.32 D11 0.87 2.62 3.11 Aspheric Coefficients: R2 K = −1.30000e+00B = 1.19770e−01 C = 6.17069e−02 D = −1.61837e−01 E = 1.55951e−01 F =−4.47577e−02 R6 K = −6.96530e−02 B = −6.61431e−02 C = −4.49055e−02 D =−6.81707e−02 E = −4.05399e−02 F = 0.00000e+00*Aspheric Surface

Numerical Example 13: f = 1-2.83 Fno = 2.86-4.90 2ω = 59.5°-22.8° R1 =9.686 D1 = 0.21 N1 = 1.802380 ν1 = 40.8 R2 = 0.838* D2 = 0.31 R3 = 1.532D3 = 0.29 N2 = 1.846660 ν2 = 23.9 R4 = 4.456 D4 = Variable R5 = Stop D5= 0.11 R6 = 0.884* D6 = 0.44 N3 = 1.743300 ν3 = 49.3 R7 = −3.817 D7 =0.10 N4 = 1.603420 ν4 = 38.0 R8 = 0.715 D8 = 0.09 R9 = 2.243 D9 = 0.09N5 = 1.698947 ν5 = 30.1 R10 = 0.828 D10 = 0.31 N6 = 1.603112 ν6 = 60.6R11 = −3.729 D11 = Variable R12 = 2.648 D12 = 0.21 N7 = 1.603112 ν7 =60.6 R13 = 44.247 D13 = 0.43 R14 = ∞ D14 = 0.44 N8 = 1.516330 ν8 = 64.1R15 = ∞ Variable Focal Length Separation 1.00 2.40 2.83 D4 2.60 0.540.32 D11 0.77 2.54 3.05 Aspheric Coefficients: R2 K = −1.30000e+00 B =1.18880e−01 C = 8.30828e−02 D = −2.46182e−01 E = 3.32011e−01 F =−1.68932e−01 R6 K = −9.46702e−02 B = −7.14402e−02 C = −3.93806e−02 D =−9.10926e−02 E = −4.05399e−02 F = 0.00000e+00*Aspheric Surface

Numerical Example 14: f = 1-2.83 Fno = 2.86-4.90 2ω = 58.0°-22.2° R1 =40.701 D1 = 0.21 N1 = 1.806100 ν1 = 40.7 R2 = 0.876* D2 = 0.28 R3 =1.641 D3 = 0.31 N2 = 1.846660 ν2 = 23.9 R4 = 7.676 D4 = Variable R5 =Stop D5 = 0.11 R6 = 0.797* D6 = 0.37 N3 = 1.743300 ν3 = 49.3 R7 = 38.519D7 = 0.08 N4 = 1.647689 ν4 = 33.8 R8 = 0.674 D8 = 0.09 R9 = 2.419 D9 =0.07 N5 = 1.846660 ν5 = 23.9 R10 = 1.359 D10 = 0.25 N6 = 1.603112 ν6 =60.6 R11 = −2.632 D11 = Variable R12 = 3.108* D12 = 0.24 N7 = 1.589130ν7 = 61.3 R13 = −25.016 D13 = 0.42 R14 = ∞ D14 = 0.43 N8 = 1.516330 ν8 =64.1 R15 = ∞ Variable Focal Length Separation 1.00 2.39 2.83 D4 2.580.51 0.27 D11 0.72 2.55 3.04 Aspheric Coefficients: R2 K = −2.25821e+00B = 2.69487e−01 C = −1.72442e−01 D = 1.53228e−01 E = −1.20333e−01 F =4.19943e−02 R6 K = −9.88795e−02 B = −7.77363e−02 C = −4.83226e−02 D =−1.69170e−01 E = 7.89854e−03 F = 0.00000e+00 R12 K = −2.86549e+00 B =−2.19540e−02 C = 1.90603e−01 D = −6.03124e−01 E = 7.17200e−01 F =−5.29660e−02*Aspheric Surface

Numerical Example 15: f = 1-2.95 Fno = 2.77-4.80 2ω = 61.7°-22.9° R1 =11.859 D1 = 0.23 N1 = 1.802380 ν1 = 40.7 R2 = 0.886* D2 = 0.35 R3 =1.689 D3 = 0.38 N2 = 1.846660 ν2 = 23.9 R4 = 5.373 D4 = Variable R5 =Stop D5 = 0.12 R6 = 0.868* D6 = 0.40 N3 = 1.743300 ν3 = 49.3 R7 = 2.419D7 = 0.11 N4 = 1.647689 ν4 = 33.8 R8 = 0.732 D8 = 0.12 R9 = 1.890 D9 =0.09 N5 = 1.846660 ν5 = 23.9 R10 = 1.093 D10 = 0.33 N6 = 1.603112 ν6 =60.6 R11 = −3.344 D11 = Variable R12 = 2.445 D12 = 0.27 N7 = 1.487490 ν7= 70.2 R13 = −37.684 D13 = 0.45 R14 = ∞ D14 = 0.46 N8 = 1.516330 ν8 =64.1 R15 = ∞ Variable Focal Length Separation 1.00 2.50 2.95 D4 2.980.60 0.35 D11 0.83 2.82 3.36 Aspheric Coefficients: R2 K = −1.55665e+00B = 1.47610e−01 C = −2.95829e−02 D = 3.79213e−02 E = −5.88716e−02 F =3.154797e−02 R6 K = −1.02390e−01 B = −5.07761e−02 C = −3.18134e−02 D =−5.79304e−02 E = −2.08294e−02 F = 0.00000e+00*Aspheric Surface

TABLE 4 Numerical Example Condition 12 13 14 15 (19) M3/fw 0.173 0.2410.324 0.173 (20) |f1/ft| 0.838 0.855 0.890 0.857 (21) f3/ft 1.588 1.6481.665 1.600 (22) f2/ft 0.719 0.720 0.725 0.759 (23) (R3f + R3r)/ −1.032−1.127 — −0.878 (R3f − R3r)

According to the fourth embodiment of the invention, it is possible toattain a zoom lens which is compact and small in diameter with lessconstituent lens elements, has a high variable magnification ratio andhas excellent optical performance.

Next, a video camera (optical apparatus) using, as a photographicoptical system, a zoom lens set forth in any one of the above numericalexamples 1 to 15 is described as an embodiment of the invention withreference to FIG. 61.

Referring to FIG. 61, the video camera includes a video camera body 110,a photographic optical system 111 composed of a zoom lens according tothe invention, an image sensor 112, such as a CCD, arranged to receivean object image formed through the photographic optical system 111, arecording means 113 for recording the object image received by the imagesensor 112, and a viewfinder 114 used for observing an object imagedisplayed on a display element (not shown). The display element iscomposed of a liquid crystal panel or the like, and is arranged todisplay thereon the object image formed on the image sensor 112.

As described above, by applying a zoom lens according to the inventionto an optical apparatus, such as a video camera, it is possible torealize an optical apparatus which is small in size and has high opticalperformance.

1-27. (Cancelled)
 28. A zoom lens, comprising, in order from an objectside to an image side: a first lens unit of negative optical power; asecond lens unit of positive optical power; and a third lens unit ofpositive optical power, said third lens unit consisting of one or twolenses including a positive lens, wherein a separation between saidfirst lens unit and said second lens unit and a separation between saidsecond lens unit and said third lens unit are varied to effect variationof magnification, and wherein said zoom lens satisfies the followingconditions:ndp3<1.5vdp3<70.0 where ndp3 and vdp3 are a refractive index and Abbe number,respectively, of material of the positive lens in said third lens unit.29. A zoom lens according to claim 28, wherein, during the variation ofmagnification from a wide-angle end to a telephoto end, said first lensunit moves with a locus convex toward the image side, said second lensunit moves monotonically toward the object side, and said third lensunit moves toward the image side.
 30. A zoom lens according to claim 28,wherein said first lens unit consists of a negative lens and a positivelens, the negative lens of said first lens unit being an aspheric lens.31. A zoom lens according to claim 28, wherein said zoom lens satisfiesthe following conditions:ndn1>1.70vdn1>35.0 where ndn1 and vdn1 are a refractive index and Abbe number,respectively, of material of a negative lens included in said first lensunit.
 32. A zoom lens according to claim 28, wherein said second lensunit consists of two cemented lenses.
 33. A zoom lens according to claim28, wherein said second lens unit has, on the most object side thereof,a cemented lens composed of a positive lens having a convex surfacefacing the object side and a negative lens having a concave surfacefacing the image side, a lens surface on the object side of the positivelens of the cemented lens being an aspheric surface, and said zoom lenssatisfies the following condition:0<(R 21−R 23)/(R 21+R 23)<0.1 where R21 is a radius of paraxialcurvature of the lens surface on the object side of the positive lens ofthe cemented lens, and R23 is a radius of paraxial curvature of a lenssurface on the image side of the negative lens of the cemented lens. 34.A zoom lens according to claim 28, wherein said second lens unit has apositive lens disposed on the most image side thereof, and said zoomlens satisfies the following conditions:ndp2>1.70vdp2>40.0 where ndp2 and vdp2 are a refractive index and Abbe number,respectively, of material of the positive lens of said second lens unit.35. A zoom lens according to claim 28, wherein said third lens unitconsists of one positive lens.
 36. A zoom lens according to claim 35,wherein the positive lens of said third lens unit is an asphericsurface.
 37. A zoom lens according to claim 28, wherein, during thevariation of magnification from a wide-angle end to a telephoto end,said third lens unit moves toward the object side.
 38. A zoom lensaccording to claim 28, wherein said zoom lens satisfies the followingcondition:0.25<(L 1+L 2+L 3)/L<0.45 where L is a distance, at a telephoto end,from a vertex on the object side of a lens disposed on the most objectside of said first lens unit to an image plane, L1 is a distance fromthe vertex on the object side of the lens disposed on the most objectside of said first lens unit to a vertex on the image side of a lensdisposed on the most image side of said first lens unit, L2 is adistance from a vertex on the object side of a lens disposed on the mostobject side of said second lens unit to a vertex on the image side of alens disposed on the most image side of said second lens unit, and L3 isa distance from a vertex on the object side of a lens disposed on themost object side of said third lens unit to a vertex on the image sideof a lens disposed on the most image side of said third lens unit.
 39. Azoom lens according to claim 28, wherein said zoom lens satisfies thefollowing condition:0.05<A 2/D 2<0.2 where D2 is the sum of thicknesses on an optical axisof lenses constituting said second lens unit, and A2 is the sum of airseparations included in said second lens unit. 40-59. (Cancelled)
 60. Anoptical apparatus, comprising: a zoom lens according to claim
 28. 61-63.(Cancelled)